SSNMR; 17O-enriched pyrophosphates; Freude

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74

Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):

For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.

SSNMR: 14N NQR of sulfa drugs

Solid-State NMR:

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68

Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):

The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.

SSNMR journal update - Rob - Vol 30, i.2 Sept. 2006

Solid-State NMR:

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68

Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):

The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.

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Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74

Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):

For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.

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Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105

Title: Quantitative analysis of 17O exchange and Formula Not Shown relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):

The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).

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Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123

Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):

Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.

JMR; pressurized glass inserts for MAS rotors

Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 229-232

Title: An easy way to prepare pressurized glass inserts for MAS rotors
Authors: Tallavaara, Pekkaa; Jokisaari, Jukkaa
Affiliations: a. NMR Research Group, Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 University of Oulu, Finland
Keywords: MAS rotor insert; Xenon; Liquid crystal; Porous material; Pressurised sample
Abstract (English):

A novel technique to prepare pressurized glass insert samples for MAS rotors is described. In this technique, a small drop of epoxy is added to the tip of a piston and the gas is squeezed into the insert by pressing the piston. The amount of gas, i.e., pressure, in the sample can be controlls doing it better, it's all over.

I have a post up on the Killer Year Blog on the subject. It deals with writing, but the message applies to any kind of hula hoop you're trying to keep in the air.

Andy's literature search is updated

natural abundance 43Ca SSNMR

Chemical Physics Letters
Volume 427, Issues 1-3 , 18 August 2006, Pages 201-205

Natural abundance 43Ca NMR study of calcium-containing organic solids: A model study for Ca-binding biomaterials

Abstract
As a first step for probing Ca sites in biomolecules using solid-state 43Ca NMR spectroscopy, natural abundance 43Ca NMR data of calcium-containing organic solids is reported. The 43Ca NMR interaction parameters indicate small electric field gradients and a relatively small chemical shift range for the calcium sites in these bio-related model compounds. A correlation of the 43Ca isotropic chemical shift with Ca–O distance is found: the 43Ca shift increases as the mean Ca–O distance decreases, with a strong deshielding being observed for calcium with strong Ca–O bonds (distance <2.4>

new heteronuclear decoupling sequence

Chemical Physics Letters
Volume 426, Issues 4-6, 4 August 2006, Pages 459-463

Swept-frequency two-pulse phase modulation for heteronuclear dipolar decoupling in solid-state NMR

Rajendra Singh Thakura, Narayanan D. Kurur, 1, a, and P.K. Madhu

Abstract
We introduce a heteronuclear dipolar decoupling sequence for application in solid-state nuclear magnetic resonance. The sequence, called swept-frequency two-pulse phase modulation (SWf-TPPM), is based on one of the decoupling sequences, TPPM. The sequence is robust in performance with respect to various experimental parameters, such as, the pulse flip angle, pulse phase, and offset and a comparison is made with other decoupling schemes, namely TPPM, SPINAL, and XiX, on a sample of U–13C-labelled tyrosine for magic-angle spinning speeds up to 14 kHz.

13C DQ under moderate MAS

Chemical Physics Letters
Volume 426, Issues 1-3 , 26 July 2006, Pages 187-191

Multiple-quantum 13C solid-state NMR spectroscopy under moderate magic-angle spinning

Sungsool Wia, , and Son-Jong Hwangb

Abstract
A new experimental scheme for the excitation and detection of 13C multiple-quantum (MQ) NMR signals in solids under magic-angle spinning (MAS) condition is presented. Symmetry-based dipolar DQ recoupling sequences have been concatenated by π/2 pulses to generate high-order 13C MQ coherences in dipolar coupled networks. This approach generates every order of MQ coherences at moderate MAS frequencies.

JCPA update

J. Phys. Chem. A, ASAP Article 10.1021/jp061350w S1089-5639(06)01350-8
Web Release Date: August 2, 2006

Alan Wong, Ramsey Ida, Xin Mo, Zhehong Gan, Jennifer Poh, and Gang Wu*

Abstract:

We report a solid-state 25Mg NMR spectroscopic study of two magnesium-containing organic compounds: monopyridinated aqua(magnesium) phthalocyanine (MgPc·H2O·Py) and chlorophyll a (Chla). Each of these compounds contains a Mg(II) ion coordinating to four nitrogen atoms and a water molecule in a square-pyramidal geometry. Solid-state 25Mg NMR spectra for MgPc·H2O·Py were obtained at 11.7 T (500 MHz for 1H) for a 25Mg-enriched sample (99.1% 25Mg atom) using both Hahn-echo and quadrupole Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences. Solid-state 25Mg NMR spectra for Chla were recorded at 25Mg natural abundance (10.1%) at 19.6 T (830 MHz for 1H). The 25Mg quadrupole parameters were determined from spectral analyses: MgPc·H2O·Py, CQ = 13.0 ± 0.1 MHz and Q = 0.00 ± 0.05; Chla, CQ = 12.9 ± 0.1 MHz and Q = 1.00 ± 0.05. This work represents the first time that Mg(II) ions in a square-pyramidal geometry have been characterized by solid-state 25Mg NMR spectroscopy. Extensive quantum mechanical calculations for electric-field-gradient (EFG) and chemical shielding tensors were performed at restricted Hartee-Fock (RHF), density functional theory (DFT), and second-order Mller-Plesset perturbation theory (MP2) levels for both compounds. Computed 25Mg nuclear quadrupole coupling constants at the RHF and MP2 levels show a reasonable basis-set convergence at the cc-pV5Z basis set (within 7% of the experimental value); however, B3LYP results display a drastic divergence beyond the cc-pVTZ basis set. A new crystal structure for MgPc·H2O·Py is also reported.

Organometallics, 25 (9), 2248 -2252, 2006

A 13C CP/MAS NMR Study of the Structure and Dynamics of [(5-C5H5)2Fe2(CO)4] Included in -Cyclodextrin: Evidence for Terminal-Bridging Exchange in the cis Isomer

Holly C. Canuto, Admir Masic, Nicholas H. Rees, Stephen J. Heyes, Roberto Gobetto, and Silvio Aime

Abstract:

The novel inclusion compound of -cyclodextrin with the binuclear metal carbonyl complex (5-C5H5)2Fe2(CO)4 as guest molecule is reported. 13C CP/MAS NMR spectroscopy, in the temperature range 100 to 353 K, is used to probe the structure and dynamics of the included molecules. Specifically, below ca. 240 K evidence is presented for the existence of both cis and trans isomers of included (5-C5H5)2Fe2(CO)4. Analysis of the temperature-dependence of the NMR line shapes shows that the microenvironment provided by the -cyclodextrin cavity allows much more extensive dynamic rearrangements of the guest molecules, in comparison to pure cis- or trans-(5-C5H5)2Fe2(CO)4, for which no isomerization or bridging-terminal carbonyl exchange processes are observed in this temperature regime. Notably, even at 100 K, bridging-terminal carbonyl exchange for the included trans isomer is rapid on the exchange-broadening time scale. However, the inclusion cavity is still more dynamically restrictive than a solution environment, and the rates of various exchange processes are usefully modified compared to those detected in solution. For (5-C5H5)2Fe2(CO)4 included in -cyclodextrin, contrary to the situation found in solution, the rate of bridging-terminal carbonyl exchange in the cis isomer is greater than the rate of cis-trans isomerization; in solution direct bridging-terminal exchange in the cis isomer could not be studied because indirect exchange via isomerization to the trans form, which undergoes rapid bridging-terminal exchange, is always significantly faster. By restricting isomerization, the inclusion environment thus confirms for the first time that the cis isomer is capable of carbonyl exchange and would allow the study of its rate and activation parameters.

Organometallics, 25 (14), 3428 -3434, 2006

Convergent Synthesis and Characterization of Organotin Dendrimers Sn{(CH₂)_nSn[(CH₂)₄SnPh₃]₃}₄ (n = 3, 4)

Herbert Schumann,* Yilmaz Aksu, and Birgit C. Wassermann

Abstract:

The reaction of the haloalkyltin trihalides Br(CH₂)₃SnBr₃ and Br(CH₂)₄SnBr₃ with 3 equiv of but-3-enylmagnesium bromide yielded Br(CH₂)₃Sn(CH₂CH₂CH=CH₂)₃ (3) and Br(CH₂)₄Sn(CH₂CH₂CH=CH₂)₃ (4). Both dendritic branches can be converted into their corresponding Grignard reagents, whose consequent treatment with 0.25 M amounts of SnCl₄₂)₃Sn(CH₂CH₂CH=CH₂)₃]₄ (5) and Sn[(CH₂)₄Sn(CH₂CH₂CH=CH₂)₃]₄ (6), respectively. The subsequent hydrostannation of 5 and 6 delivered Sn{(CH₂)₃Sn[(CH₂)₄SnPh₃]₃}₄ (7) and Sn{(CH₂)₄Sn[(CH₂)₄SnPh₃]₃}₄ (8) as dendrimers of the second generation. All compounds were characterized by elemental analysis, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy, and MALDI-TOF mass spectrometry. resulted in the formation of the dendrimers Sn[(CH

Organometallics, 25 (14), 3370 -3378, 2006

Comment P-31 NMR and p31-pt J-coupling

Platinum(II) Phosphido Complexes as Metalloligands. Structural and Spectroscopic Consequences of Conversion from Terminal to Bridging Coordination

Corina Scriban, Denyce K. Wicht, David S. Glueck, Lev N. Zakharov, James A. Golen, and Arnold L. Rheingold

Abstract:

Treatment of the terminal phosphido complexes Pt(dppe)(Me)(PPh(R)) (R = Ph (1), i-Bu (6)) with Pt(dppe)(Me)(OTf) gave the cationic phosphido complexes [(Pt(dppe)(Me))₂(PPh(R))][OTf] (R = Ph (7), i-Bu (8)). Similarly, Pt((R,R)-Me-Duphos)(Me)(PPh(i-Bu)) (10) was converted to [(Pt((R,R)-Me-Duphos)(Me)) ₂ (PPh(i-Bu))][OTf] (11). A fluxional process in 8 and 11, presumably involving hindered rotation about the Pt-PPh(i-Bu) bonds, was observed by NMR spectroscopy; it resulted in two diastereomers for 8 and four for 11 at low temperature. Coordination of the metalloligand 10 to the [Pt((R,R)-Me-Duphos)(Me)]⁺11, resulted in structural changes at the Pt-phosphido group, whose geometry changed from distorted pyramidal to tetrahedral. Decomposition of 6 also gave the cation 8, while oxidation of 6 with H₂O₂ gave the crystallographically characterized phosphido oxide complex Pt(dppe)(Me)(P(O)Ph(i-Bu)) (12).

Chemistry - A European Journal, Volume: 12, Issue: 20 , pp. 5282 - 5292

Solid-State NMR and EXAFS Spectroscopic Characterization of Polycrystalline Copper(I) O,O’-Dialkyldithiophosphate Cluster Compounds: Formation of Copper(I) O,O’-Diisobutyldithiophosphate Compounds on the Surface of Synthetic Chalcocite I) Rusanova, Daniela; Pike, Kevin J.; Persson, Ingmar; Hanna, John V.; Dupree, Ray; Forsling,

Abstract: A number of polycrystalline copper(i) O,O’-dialkyldithiophosphate cluster compounds with Cu4, Cu6, and Cu8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy.The structural relationship of these compounds is discussed. The polyACHTUNGTRENUNGcrystalline copper(i) O,O’-diisobutyl ACHTUNG- TRENUNGdithiophosphate cluster compounds,[Cu8ACHTUNGTRENUN {S2PACHTUNG- TRENUNG(OiBu)2}6(S)]and [Cu6ACHTUNGTRENUNG{S2PACHTUNGTRENUNG(OiBu)2}6], were also characterized by using 31P CP/MAS NMR CP = cross polarization, MAS =magic-angle spinning) and static 65Cu NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the 31P chemical-shifttensor, and the 65Cu chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR
spectra of the polycrystalline copper(i) cluster compounds, are presented. The adsorption mechanism of the potassium O,O’-diACHTUNGTRENUNGisobutyldithiophosphate collector, KACHTUNGTRENUNG[S2PACHTUNGTRENUNG(OiBu)2], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). 31P NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu8ACHTUNGTRENUNG {S2PACHTUNGTRENUNG (OiBu)2}- 6(S)]and [Cu6- ACHTUNGTRENUNG{S2PACHTUNGTRENUNG(OiBu)2}6]compounds .

J. Chem. Phys. 125, 044510

Description of depolarization effects in double-quantum solid state nuclear magnetic resonance experiments using multipole-multimode Floquet theory

Ramesh Ramachandran and Robert G. Griffin


Using an analytical model based on multipole-multimode Floquet theory (MMFT), we describe the polarization loss (or depolarization) observed in double-quantum (DQ) dipolar recoupling magic angle spinning (MAS) experiments. Specifically, the factors responsible for depolarization are analyzed in terms of higher order corrections to the spin Hamiltonian in addition to the usual phenomenological decay rate constant. From the MMFT model and the effective Hamiltonians, we elucidate the rationale behind the inclusion of a phenomenological damping term in DQ recoupling experiments. As a test of this theoretical approach, the recoupling efficiency of one class of 13C–13C and 13C–15N resonance width dipolar recoupling experiments are investigated at different magnetic field strengths and compared with the more exact numerical simulations. In contrast to existing analytical treatments, the role of higher order corrections is clearly explained in the context of the MMFT approach leading to a better understanding of the underlying spin physics. Furthermore, the analytical model presented herein provides a general framework for describing coherent and incoherent effects in homonuclear and heteronuclear DQ MAS recoupling experiments.

J. Chem. Phys. 125, 034507

Heteronuclear isotropic mixing separated local field NMR spectroscopy

Sergey V. Dvinskikh, Kazutoshi Yamamoto and Ayyalusamy Ramamoorthy

This paper presents a theoretical, numerical, and experimental study of a new class of separated local field (SLF) techniques. These techniques are based on the heteronuclear isotropic mixing leading to spin exchange via the local field (HIMSELF). It is shown that highly efficient and robust SLF experiments can be designed based on double channel windowless homonuclear decoupling sequences. Compared to rotating frame techniques based on Hartmann-Hahn cross polarization, the new approach is less susceptible to the frequency offset and chemical shift interaction and can be applied in the structural studies of macromolecules that are uniformly labeled with isotopes such as 13C and 15N. Furthermore, isotropic mixing sequences allow for transfer of any magnetization component of one nucleus to the corresponding component of its dipolar coupled partner. The performance of HIMSELF is studied by analysis of the average Hamiltonian and numerical simulation and is experimentally demonstrated on a single crystalline sample of a dipeptide and a liquid crystalline sample exhibiting motionally averaged dipolar couplings.

J. Chem. Phys. 124, 204717

Nuclear magnetic resonance structural investigations of ammonia-doped fullerides
T. Shiroka, G. Fumera, O. Ligabue, and M. Riccò G. C. Antonioli

The dynamic and structural properties of the ammonia-doped superconducting fulleride (NH3)xNaK2C60 (0.5x1), well known for its anomalous decrease of transition temperature with doping, have been investigated using sodium and deuterium solid-state NMR techniques. The independence of 23Na quadrupole splitting from the ammonia content x, which, at the same time, substantially affects Tc, suggests a marginal role of the cation position in the superconducting mechanism. On the other hand, a strong reduction of the deuterium quadrupole coupling with respect to the free ammonia value denotes the presence of weak hydrogen bonds between the deuterium atoms and fullerene orbitals. Despite the bond weakness, as evinced by the lively ammonia rotational dynamics even at very low temperatures, the resulting electron localization could explain the observed Tc anomaly. The motion of the ND3–Na group (located in the compound's octahedral voids), as well as the evolution of the ammonia dynamics as a function of temperature, were determined from deuterium NMR line shape analysis and from detailed numerical simulations. While at the lowest measured temperatures only the ammonia rotation around its own C3 axis takes place, above ~25 and 70 K, respectively, also the wobbling of the C3 axis and the ND3 relocation become active, successfully modeled by a strongly correlated motion involving two different time scales

Phys. Chem. Chem. Phys., 2006, 8, 3552 - 3556

Reactions of alkyl-radicals with gold and silver nanoparticles in aqueous solutions

Tomer Zidki, Haim Cohen and Dan Meyerstein

Comment: This paper doen not have NMR in it.

Silver and gold nanoparticles are very efficient catalysts for the dimerization of methyl-radicals in aqueous solutions. The rate constants for the reaction of methyl-radicals with the gold and silver nanoparticles were measured and found to be 3.7 × 108 M–1 s–1 and 1.4 × 109 M–1 s–1, respectively. The results thus suggest that alkyl-radicals, also not reducing ones, are scavenged by these nanoparticles. This might explain the role, if such a role exists, of these nanoparticles in medical applications.

Phys. Chem. Chem. Phys., 2006, 8, 3510 - 3519

Solid state NMR studies of photoluminescent cadmium chalcogenide nanoparticles

Christopher I. Ratcliffe, Kui Yu, John A. Ripmeester, Md. Badruz Zaman, Cristina Badarau and Shanti Singh

Solid state 113Cd, 77Se, 13C and 31P NMR have been used to study a number of Cd chalcogenide nanoparticles synthesized in tri-n-octyl-phosphine (TOP) with different compositions and architectures. The pure CdSe and CdTe nanoparticles show a dramatic, size-sensitive broadening of the 113Cd NMR line, which can be explained in terms of a chemical shift distribution arising from multiple Cd environments. From 13C NMR, it has been discovered that TOP, or its derivatives such as TOPO (trioctylphosphine oxide), is rapidly moving about the surface of the nanoparticles, indicating that it is relatively weakly bound as compared to other materials used as surface ligands, such as hexadecylamine. 31P NMR of the nanoparticles shows at least five species arising from coordination of the ligands to different surface sites. 113Cd NMR of CdSeTe alloy and layered nanoparticles has provided crucial information which, in conjunction with results from other techniques (especially optical characterization), has made it possible to develop a detailed picture of the composition and structure of these materials: (i) a true CdSeTe homogeneous alloy nanoparticle, (ii) a nanoparticle segregated into an alloy core region rich in Te, with a CdSeTe (close to 1 : 1 Se : Te) alloy shell and (iii) a CdSe/CdTe/CdSe layered nanoparticle in which the CdTe layer contains a small amount of Se and which forms a Quantum Dot Quantum Well (QDQW) system. The results demonstrate that solid state NMR is a vital tool in the arsenal of characterisation techniques available for nanomaterials.

Phys. Chem. Chem. Phys., 2006, 8, 3423 - 3431

23Na multiple-quantum MAS NMR of the perovskites NaNbO3 and NaTaO3

Sharon E. Ashbrook, Laurent Le Pollès, Régis Gautier, Chris J. Pickard and Richard I. Walton

The distorted perovskites NaTaO3 and NaNbO3 have been studied using 23Na multiple-quantum (MQ) MAS NMR. NaTaO3 was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO3 were studied. The first, a commercially available sample which was annealed at 900 °C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state.

Phys. Chem. Chem. Phys., 2006, 8, 3418 - 3422

Assigning powders to crystal structures by high-resolution 1H–1H double quantum and 1H–13C J-INEPT solid-state NMR spectroscopy and first principles computation. A case study of penicillin G

Nicolas Mifsud, Bénédicte Elena, Chris J. Pickard, Anne Lesage and Lyndon Emsley

We show how powder samples at natural isotopic abundance can be assigned to crystal structures by using high-resolution proton and carbon-13 solid-state NMR spectra in combination with first principles calculations. Homonuclear proton double-quantum spectra in combination with through-bond proton–carbon HSQC spectra are used to assign the NMR spectra. We then show that the proton chemical shifts can be included in the process of assigning the spectra to a crystal structure using first principles calculations. The method is demonstrated on the K salt of penicillin G.

Phys. Chem. Chem. Phys., 2006, 8, 3379 - 3382

Spin–spin coupling constants in homonuclear polynitrogen species

David L. Bryce

Quantum chemical calculations provide new insights into the dependence of J(N,N) coupling tensors on bonding environment in a series of polynitrogen species including N5+.

Phys. Chem. Chem. Phys., 2006, 8, 2733 - 2743

An NMR and relativistic DFT investigation of one-bond nuclear spin–spin coupling in solid triphenyl group-14 chlorides

Mathew J. Willans, Bryan A. Demko and Roderick E. Wasylishen

A solid-state nuclear magnetic resonance and zeroth-order regular approximation density functional theory, ZORA-DFT, study of one-bond nuclear spin–spin coupling between group-14 nuclei and quadrupolar 35/37Cl nuclei in triphenyl group-14 chlorides, Ph3XCl (X = C, Si, Ge, Sn and Pb), is presented. This represents the first combined experimental and theoretical systematic study of spin–spin coupling involving spin-pairs containing quadrupolar nuclei. Solid-state NMR spectra have been acquired for all compounds in which X has a spin-1/2 isotope—13C, 29Si, [117/119]Sn and 207Pb—at applied magnetic fields of 4.70, 7.05 and 11.75 T. From simulations of these spectra, values describing the indirect spin–spin coupling tensor—the isotropic indirect spin–spin coupling constant, 1J(X,35/37Cl)iso and the anisotropy of the J tensor, 1J(X,35/37Cl)—have been determined for all but the lead–chlorine spin-pair. To better compare the indirect spin–spin coupling parameters between spin-pairs, 1Jiso and 1J values were converted to their reduced coupling constants, 1Kiso and 1K. From experiment, the sign of 1Kiso was found to be negative while the sign of 1K is positive for all spin-pairs investigated. The magnitude of both 1Kiso and 1K was found to increase as one moves down group-14. Theoretical values of the magnitude and sign of 1Kiso and 1K were obtained from ZORA-DFT calculations and are in agreement with the available experimental data. From the calculations, the Fermi-contact mechanism was determined to provide the largest contribution to 1Kiso for all spin-pairs while spin-dipolar and paramagnetic spin–orbit mechanisms make significant contributions to the anisotropy of K. The inclusion of relativistic effects was found to influence K(Sn,Cl) and K(Pb,Cl).

Phys. Chem. Chem. Phys., 2006, 8, 2635 - 2641

Phys. Chem. Chem. Phys., 2006, 8, 2635 - 2641, DOI: 10.1039/b601539e

Magnetic alignment of aqueous CTAB in nematic and hexagonal liquid crystalline phases investigated by spin-1 NMR

Jacalyn S. Clawson, Gregory P. Holland and Todd M. Alam

Spin-1 NMR has been used to characterize the magnetically aligned nematic and hexagonal liquid crystalline phases of aqueous cetyltrimethylammonium bromide (CTAB). A nematic/hexagonal biphasic region has been identified for the first time in this system. The nematic phase is characterized by an order parameter of smaller magnitude and greater temperature dependence. Magnetic alignment kinetic rates of the two phases differ greatly, with the nematic phase showing magnetic alignment much faster than the hexagonal phase. Equilibration has been monitored over time by measuring the change in quadrupole splitting as a function of temperature. As the sample equilibrates the temperature dependence of the splitting decreases logarithmically. This work also demonstrates how the phase and order of the liquid crystal can be manipulated during the early part of equilibration.

Joel - Monthly Journal Update

Probing Local Environments in Paramagnetic Europium-Substituted Keggin Solids by 31P Magic Angle Spinning NMR Spectroscopy
W. Huang et al.
J.Phys.Chem.B(2006)110,12340.

Abstract:
Paramagnetic Eu-substituted Keggin oxopolytungstates crystallize in different forms, determined by the nature of the counterions. The crystal packing is in turn responsible for the variations in the geometry of paramagnetic Eu sites with respect to the anion core. We probed the paramagnetic environments in a series of Eu-substituted Keggin solids, by 31P magic angle spinning NMR spectroscopy. 31P spinning sideband envelopes are dominated by the electron-nuclear dipolar interaction. For the compounds under investigation, both the magnitude and the asymmetry parameter of the electron-nuclear dipolar coupling tensor are sensitive to the mutual arrangements of paramagnetic Eu sites in the crystal lattice. and also report on the stoichiometry of the anion. The electron-nuclear dipolar coupling tensors were calculated from the crystallographic coordinates and the experimentally determined effective magnetic moments, assuming a point dipole approximation. The computed tensors are in very good agreement with the experimental spectra. Furthermore, the P-Eu distance estimates, accurate to within 0.06-0.12 A, can be obtained directly from the magnitude of the electron-nuclear dipolar coupling. This work demonstrates that 31P MAS NMR spectroscopy is a useful probe for investigating local environments in paramagnetic Keggin solids.


Cory
Oxygen Sites and Network Coordination in Sodium Germanate Glasses and Crystals: High Resolution Oxygen-17 and Sodium-23 NMR.
L.S. Du and J.F. Stebbins
J.Phys.Chem.B(2006)110,12427.

Abstract:
Sodium germanate glasses are well-studied materials in which, unlike silicates but analogous to borates, the major structural consequence of alkali addition is generally thought to involve a coordination number increase of the network-forming Ge cations. However, the nature of this change, in particular quantifying fractions of nonbridging oxygens and of five- and/or six-coordinated Ge, has remained unresolved. We present here highresolution 17O results, including triple-quantum MAS NMR (3QMAS), on a series of crystalline model compounds that allow the definition of ranges of chemical shifts corresponding to oxygens bonded to various coordinations of Ge. These include quartz- and rutile-structured GeO2, Na4Ge9O20, Na2Ge4O9, and Na2GeO3 (germanium dioxide, sodium enneagermanate, sodium tetragermanate, and sodium metagermanate). 3QMAS spectra of Na-germanate glasses ranging from 0% to 27% Na2O clearly show the development of partially resolved peaks as alkali is added, corresponding to signals from nonbridging oxygens (in the highest Na glasses) and to oxygen bridging between one four-coordinated and one higher coordinated Ge. As in conventional models of this system, nonbridging oxygen contents are much lower than in corresponding silicates. Although we do not directly distinguish between five- and six-coordinated Ge, modeling of bridging oxygen populations and comparison with measured speciation suggest that substantial proportions of both species are likely to be present. High-field 23Na MAS NMR shows systematic decreases in mean Na-O bond distance and/or coordination number with increasing alkali content that can be compared with published results for high-temperature liquids. These results, as well as comparison of molar volumes of glasses and high-temperature liquids, suggest the possibility of significant temperature effects on liquid structure.

Andy
Photochemical Fine-Tuning of Luminescent Coloout on Cadmium Selenide Nanoparticles: Fabricating a Single-Source Multicolor Luminophore.
T. Torimoto et al.
J.Phys.Chem.B(2006)110,13314.

Abstract:
Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/ CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.

Josh, Andy
Synthesis, crystal structure and magnetic properties of an alternating manganese chain.
M.R. Silva et al.
JSolidStateChem (2006) 179, 2054.

Abstract:
A new 1D complex has been prepared and characterized. X-ray single crystal structure con.rms that the Mn(II) ions assemble in alternating chains with Mn–Mn distances of 3.8432(13) and 4.4428(14)A . A 3D network of hydrogen bonds links the chains together. The temperature dependence of the magnetic susceptibility reveals that this compound undergoes a magnetic transition and exhibits an antiferromagnetic interaction in the low-temperature phase with two alternating exchange interactions of -2.32(1) and -5.55(1)cm-1.

Rob
Sr4PbPt4O11, the first platinum oxide containing Pt2 6+ ions.
C. Renard et al.
JSolidStateChem (2006) 179, 2054.

Abstract:
We report the synthesis and crystal structure of the new compound Sr4PbPt4O11, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R = 0.0260 and wR = 0.0262. The symmetry is triclinic, space group P1¯ , with a = 5.6705(6) A, b = 9.9852(5) A, c = 10.0889(5) A, alpha = 90.421(3), beta = 89.773(8), gamma = 90.140(9) and Z = 2. The structure is built from dumbell-shaped Pt2O9 entities formed by a dinuclear metal–metal bonded Pt2 6+ ion with asymmetric environments of the two Pt atoms, classical PtO4 square plane and unusual PtO5 square pyramid. Successive Pt2O9 entities deduced from 901 rotations are connected through the oxygens of the PtO4 basal squares to form (Pt4O10)-8 columns further connected through Pb2+ and Sr2+ ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.

Structural and 31P NMR investigation of Bi(MM')2PO6 statistic solid solutions: Deconvolution of lattice constrants and cationic influences.
M. Colmont et al.
JSolidStateChem (2006) 179, 2111.

Abstract:
Two solid solutions BiMxMg(2-x)PO6 (with M2+ = Zn or Cd) have been studied through 31P MAS NMR. The analysis has been performed on the basis of re.ned crystal structures through X-ray diffraction and neutron diffraction. The BiZnxMg(2-x)PO6 does not provide direct evidence for sensitive changes in the phosphorus local symmetry. This result is in good agreement with structural data which show nearly unchanged lattices and atomic separations through the Zn2+ for Mg2+ substitution. On the other hand, the Cd2+ for Mg2+ substitution behaves differently. Indeed, up to five resonances are observed, each corresponding to one of the five first-cationic neighbour distributions, i.e. 4Mg/0Cd, 3Mg/1Cd, 2Mg/2Cd, 1Mg/3Cd and 0Mg/4Cd. Their intensities match rather well the expected weight for each con.guration of the statistical Cd2+/Mg2+ mixed occupancy. The match is further improved when one takes into account the in.uence of the 2nd cationic sphere that is available from high-.eld NMR data (18.8 T). Finally, the fine examination of the chemical shift for each resonance versus x allows to de-convolute the mean Z/a2 effective field into two sub-effects: a lattice constraint only term and a chemical-only term whose effects are directly quantifiable.

JACS - Volume 128, Issue 27

Cory's Comment: small coils = super high (600 kHz) proton decoupling fields!

Title: Microcoil High-Resolution Magic Angle Spinning NMR Spectroscopy
Authors: Hans Janssen, Andreas Brinkmann, Ernst R. H. van Eck, P. Jan M. van Bentum, and Arno P. M. Kentgens
Page #: 8722

Abstract: We report the construction of a dual-channel microcoil nuclear magnetic resonance probehead allowing magic-angle spinning for mass-limited samples. With coils down to 235 m inner diameter, this allows high-resolution solid-state NMR spectra to be obtained for amounts of materials of a few nanoliters. This is demonstrated by the carbon-13 spectrum of a tripeptide and a single silk rod, prepared from the silk gland of the Bombyx mori silkworm. Furthermore, the microcoil allows for radio frequency field strengths well beyond current probe technology, aiding in getting the highest possible resolution by efficiently decoupling the observed nuclei from the abundantly present proton nuclei.

Cory's Journals - June 2006

Does anyone use this thing anymore???

As per usual, by the end of today, I will have the journal articles that I collected in June 2006 available in their usual spot.

Peace.

Hiyam's Journal Update

The Journal of Chemical Physics -- 28 May 2006

J. Chem. Phys. 124, 204717 (2006) (10 pages)

Nuclear magnetic resonance structural investigations of ammonia-doped fullerides

T. Shiroka, G. Fumera, O. Ligabue, and M. Riccò G. C. Antonioli

Abstract: The dynamic and structural properties of the ammonia-doped superconducting fulleride (NH₃)_xNaK₂C₆₀ (0.5<1),> NMR techniques. The independence of ²³Na quadrupole splitting from the ammonia content x, which, at the same time, substantially affects T_c, suggests a marginal role of the cation position in the superconducting mechanism. On the other hand, a strong reduction of the deuterium quadrupole coupling with respect to the free ammonia value denotes the presence of weak hydrogen bonds between the deuterium atoms and fullerene orbitals. Despite the bond weakness, as evinced by the lively ammonia rotational dynamics even at very low temperatures, the resulting electron localization could explain the observed T_c anomaly. The motion of the ND₃–Na group (located in the compound's octahedral voids), as well as the evolution of the ammonia dynamics as a function of temperature, were determined from deuterium NMR line shape analysis and from detailed numerical simulations. While at the lowest measured temperatures only the ammonia rotation around its own C₃ axis takes place, above ~25 and 70 K, respectively, also the wobbling of the C₃ axis and the ND₃ relocation become active, successfully modeled by a strongly correlated motion involving two different time scales. ©2006 American Institute of Physics

The Journal of Chemical Physics -- 14 June 2006

J. Chem. Phys. 124, 224106 (2006) (7 pages)

Relativistic calculation of nuclear magnetic shielding using normalized elimination of the small component K. Kudo, H. Maeda, T. Kawakubo, Y. Ootani, M. Funaki, and H. Fukui

Abstract: The normalized elimination of the small component (NESC) theory, recently proposed by Filatov and Cremer [J. Chem. Phys. 122, 064104 (2005)], is extended to include magnetic interactions and applied to the calculation of the nuclear magnetic shielding in HX (X=F,Cl,Br,I) systems. The NESC calculations are performed at the levels of the zeroth-order regular approximation (ZORA) and the second-order regular approximation (SORA). The calculations show that the NESC-ZORA results are very close to the NESC-SORA results, except for the shielding of the I nucleus. Both the NESC-ZORA and NESC-SORA calculations yield very similar results to the previously reported values obtained using the relativistic infinite-order two-component coupled Hartree-Fock method. The difference between NESC-ZORA and NESC-SORA results is significant for the shieldings of iodine. ©2006 American Institute of Physics

Physical Chemistry Chemical Physics, 2006, 8, 1394 - 1403
DOI: 10.1039/b516765e

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Molecular dynamics and ordering of pyridine in its cyclophosphazene inclusion compound as evaluated by solid state ²H NMR spectroscopy

Jorge A. Villanueva-Garibay and Klaus Müller

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Variable temperature ²H NMR experiments (line shape analysis, relaxation studies) were carried out on the pyridine-d₅–tris-(1,2-dioxyphenyl)-cyclotriphosphazene inclusion compound in the temperature range between 110–300 K. It is found that the pyridine guests are highly mobile throughout the whole temperature range covered here. The observation of three superimposed ²H NMR signals can be understood in terms of a particular (motionally averaged) orientation of the pyridine molecules, which is a consequence of the molecular symmetry of the pyridine guests and the imposed channel restrictions. The experimental data are consistent with a combined rotation on cone–small angle fluctuation model, which assumes a fast molecular reorientation between two superimposed cones with an opening angle for the inner cone between 59–73° (angle of fluctuation between 1–3°). On the basis of this model assumption it is possible to reproduce both the experimental ²H NMR line shapes and the spin–lattice relaxation data in a quantitative way. The analysis of the partially relaxed spectra (inversion recovery experiments) yields the correlation times for this overall motional process. They follow an Arrhenius behavior from which an activation energy of 8.7 ± 0.4 kJ mol^–1 is derived. The results are discussed in the framework of the published data for related systems.

Joel: Journal Updates

Hiyam and Andy
89Y Magic Angle Spinning NMR of Y2Ti2-xSnxO7 Pyrochlores
S.E. Ashbrook, K.R. Whittle, G.R.Lumpkin and I. Farnan
J.Phys.Chem.B (2006)110, 9324.

Abstract:
The yttrium local environment in the series of pyrochlores Y2Ti2-xSnxO7 was studied using 89Y NMR. Oxides with the pyrochlore structure exhibit a range of interesting physical and chemical properties, resulting in many technological applications, including the encapsulation of lanthanide- and actinide-bearing radioactive waste. The use of the nonradioactive Y3+ cation provides a sensitive probe for any changes in the local structure and ordering with solid solution composition, through 89Y (I ) 1/2) NMR. We confirm that a single pyrochlore phase is formed over the entire compositional range, with Y found only on the eight-coordinated A site. A significant (15 ppm) chemical shift is observed for each Sn substituted into the Y second neighbor coordination environment. The spectral signal intensities of the possible combinations of Sn/Ti neighbors match those predicted statistically assuming a random distribution of Sn4+/Ti4+ on the six-coordinated pyrochlore B site.


Acidity of Mesoporous MoOx/ZrO2 and WOx/ZrO2 Materials: A Combined Solid-State NMR and Theoretical Calculation Study
J. Xu et al.
J.Phys.Chem.B (2006)110, 10662.

Abstract:
The acidity of mesoporous MoOx/ZrO2 and WOx/ZrO2 materials was studied in detail by multinuclear solidstate NMR techniques as well as DFT quantum chemical calculations. The 1H MAS NMR experiments clearly revealed the presence of two different types of strong Brønsted acid sites on both MoOx/ZrO2 and WOx/ZrO2 mesoporous materials, which were able to prontonate adsorbed pyrine-d5 (resulting in 1H NMR signals at chemical shifts in the range 16-19 ppm) as well as adsorbed trimethylphosphine (giving rise to 31P NMR signal at ca. 0 ppm). The 13C NMR of adsorbed 2-13C-acetone indicated that the average Brønsted acid strength of the two mesoporous materials was stronger than that of zeolite HZSM-5 but still weaker than that of 100% H2SO4, which was in good agreement with theoretical predictions. The quantum chemical calculations revealed the detailed structures of the two distinct types of Brønsted acid sites formed on the mesoporous MoOx/ZrO2 and WOx/ZrO2. The existence of both monomer and oligomer Mo (or W) species containing a Mo-OH-Zr (or W-OH-Zr) bridging OH group was confirmed with the former having an acid strength close to zeolite HZSM-5, with the latter having an acid strength similar to sulfated zirconia. On the basis of our NMR experimental and theoretical calculation results, a possible mechanism was proposed for the formation of acid sites on these mesoporous materials.

Hiyam
Determinations of 15N Chemical Shift Anisotropy Magnitudes in a Uniformly 15N,13C-Labeled Microcrystalline Protein by Three-Dimensional Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy
B.J. Wylie, W.T. Franks, and C.M. Rienstra
J.Phys.Chem.B (2006)110, 10936.

Abstract:
Amide 15N chemical shift anisotropy (CSA) tensors provide quantitative insight into protein structure and dynamics. Experimental determinations of 15N CSA tensors in biologically relevant molecules have typically been performed by NMR relaxation studies in solution, goniometric analysis of single-crystal spectra, or slow magic-angle spinning (MAS) NMR experiments of microcrystalline samples. Here we present measurements of 15N CSA tensor magnitudes in a protein of known structure by three-dimensional MAS solid-state NMR. Isotropic 15N, 13CR, and 13C¢ chemical shifts in two dimensions resolve site-specific backbone amide recoupled CSA line shapes in the third dimension. Application of the experiments to the 56-residue ‚1 immunoglobulin binding domain of protein G (GB1) enabled 91 independent determinations of 15N tensors at 51 of the 55 backbone amide sites, for which 15N-13CR and/or 15N-13C¢ cross-peaks were resolved in the two-dimensional experiment. For 37 15N signals, both intra- and interresidue correlations were resolved, enabling direct comparison of two experimental data sets to enhance measurement precision. Systematic variations between ‚-sheet and R-helix residues are observed; the average value for the anisotropy parameter, ‰ (‰ ) ‰zz - ‰iso), for R-helical residues is 6 ppm greater than that for the ‚-sheet residues. The results show a variation in ‰ of 15N amide backbone sites between -77 and -115 ppm, with an average value of -103.5 ppm. Some sites (e.g., G41) display smaller anisotropy due to backbone dynamics. In contrast, we observe an unusually large 15N tensor for K50, a residue that has an atypical, positive value for the backbone torsion angle. To our knowledge, this is the most complete experimental analysis of 15N CSA magnitude to date in a solid protein. The availability of previous high-resolution crystal and solution NMR structures, as well as detailed solid-state NMR studies, will enhance the value of these measurements as a benchmark for the development of ab initio calculations of amide 15N shielding tensor magnitudes.


Another Rod paper
Grand Canonical Monte Carlo Simulations of the 129Xe NMR Line Shapes of Xenon Adsorbed in ((+/-)-[Co(en)3]Cl3
D.N. Sears, R.E. Wasylishen, and T. Ueda
J.Phys.Chem.B (2006)110, 11120.

Abstract:
The 129Xe NMR line shapes of xenon adsorbed in the nanochannels of the (()-[Co(en)3]Cl3 ionic crystal have been calculated by grand canonical Monte Carlo (GCMC) simulations. The results of our GCMC simulations illustrate their utility in predicting 129Xe NMR chemical shifts in systems containing a transition metal. In particular, the nanochannels of (()-[Co(en)3]Cl3 provide a simple, yet interesting, model system that serves as a building block toward understanding xenon chemical shifts in more complex porous materials containing transition metals. Using only the Xe-C and Xe-H potentials and shielding response functions derived from the Xe@CH4 van der Waals complex to model the interior of the channel, the GCMC simulations correctly predict the 129Xe NMR line shapes observed experimentally (Ueda, T.; Eguchi, T.; Nakamura, N.; Wasylishen, R. E. J. Phys. Chem. B 2003, 107, 180-185). At low xenon loading, the simulated 129Xe NMR line shape is axially symmetric with chemical-shift tensor components ‰| ) 379 ppm and ‰^ ) 274 ppm. Although the simulated isotropic chemical shift, ‰iso ) 309 ppm, is overestimated, the anisotropy of the chemical-shift tensor is correctly predicted. The simulations provide an explanation for the observed trend in the 129Xe NMR line shapes as a function of the overhead xenon pressure: ‰^ increased from 274 to 292 ppm, while ‰| changed by only 3 ppm over the entire xenon loading range. The overestimation of the isotropic chemical shifts is explained based upon the results of quantum mechanical 129Xe shielding calculations of xenon interacting with an isolated (()-[Co(en)3]Cl3 molecule. The xenon chemical shift is shown to be reduced by about 12% going from the Xe@[Co(en)3]Cl3 van der Waals complex to the Xe@C2H6 fragment.

JACS: Ashbrook and Wimperis; 27Al MQMAS and STMAS as probes of dynamics in microporous solids

J. Am. Chem. Soc., 128 (24), 8054 -8062, 2006. 10.1021/ja057682g S0002-7863(05)07682-1

Dynamics on the Microsecond Timescale in Microporous Aluminophosphate AlPO-14 as Evidenced by 27Al MQMAS and STMAS NMR Spectroscopy

Sasa Antonijevic, Sharon E. Ashbrook, Silke Biedasek, Richard I. Walton,* Stephen Wimperis,*# and Huaixin Yang

Contribution from the Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland, School of Chemistry and EaStCHEM, University of St Andrews, St Andrews KY16 9ST, United Kingdom, Institut für Technische und Makromolekulare Chemie, Universität Hamburg, 20146 Hamburg, Germany, Department of Chemistry, The Open University, Milton Keynes MK7 6AA, United Kingdom, Department of Chemistry and WestCHEM, University of Glasgow, Glasgow G12 8QQ, United Kingdom, and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

r.i.walton@open.ac.uk; s.wimperis@chem.gla.ac.uk
Received November 11, 2005

Abstract:

Multiple-quantum magic angle spinning (MQMAS) and satellite-transition magic angle spinning (STMAS) are two well-known techniques for obtaining high-resolution, or "isotropic", NMR spectra of quadrupolar nuclei. It has recently been shown that dynamics-driven modulation of the quadrupolar interaction on the microsecond timescale results in linewidths in isotropic STMAS spectra that are strongly broadened, while, in contrast, the isotropic MQMAS linewidths remain narrow. Here, we use this novel methodology in an 27Al (I = 5/2) NMR study of the calcined-dehydrated aluminophosphate AlPO-14 and two forms of as-synthesized AlPO-14, one prepared with isopropylamine (C3H7NH2) as the template molecule and one with piperidine (C5H10NH). For completeness, the 31P and 13C (both I = 1/2) MAS NMR spectra are also presented. A comparison of the 27Al MQMAS and STMAS NMR results show that, although calcined AlPO-14 appears to have a rigid framework structure, the extent of motion in the two as-synthesized forms is significant, with clear evidence for dynamics on the microsecond timescale in the immediate environments of all four Al sites in each material. Variable-temperature 27Al STMAS NMR studies of the two as-synthesized AlPO forms reveal the dynamics to be complex, with the motions of both the guest water molecules and organic template molecules shown to be contributing. The sensitivity of the STMAS NMR experiment to the presence of microsecond timescale dynamics is such that it seems likely that this methodology will prove useful in NMR studies of host-guest interactions in a wide variety of framework materials.

JACS, Berger; 31P NMR, ab initio and IR; phosphorus CS tensors

J. Am. Chem. Soc., ASAP Article 10.1021/ja057085u S0002-7863(05)07085-X
Web Release Date: June 10, 2006

Copyright © 2006 American Chemical Society
Electronic Properties of Furyl Substituents at Phosphorus and Their Influence on 31P NMR Chemical Shifts

Marco Ackermann, Aurelia Pascariu, Thomas Höcher, Hans-Ullrich Siehl, and Stefan Berger*

Contribution from the Institut für Analytische Chemie, Fakultät für Chemie und Mineralogie, Universität Leipzig, Linnéstr. 3, D-04103 Leipzig, Germany and Abteilung für Organische Chemie I, Fakultät für Naturwissenschaften, Universität Ulm, D-89069 Ulm, Germany

Abstract:

The electronic properties of 2-furyl and 3-furyl substituents attached to phosphanes and phosphonium salts were studied by means of IR spectroscopy and experimental and computational 31P NMR spectroscopy. The heteroaromatic systems proved to be electron withdrawing with respect to phenyl substituents. However, phosphorus atoms with attached furyl substituents are strongly shielded in NMR. The reason for this phenomenon was studied by solid state 31P MAS NMR experiments. The chemical shift tensor was extracted, and the orientation within the molecules was determined. The tensor component 33, which is effected the most by furyl systems, is oriented perpendicular to the P-C bonds of the substituents. P-furyl bonds are shorter than P-phenyl bonds. We assume therefore a lower ground-state energy of the molecules, because of the electron withdrawing properties of the 2-furyl systems. The para component of the 31P NMR magnetic shielding is therefore smaller, which results in an overall increase of the magnetic shielding.

CPL, Blaha et al: 27Al and plane wave (WIEN) calculations

Chemical Physics Letters
Volume 424, Issues 4-6 , 24 June 2006, Pages 321-326

27Al NMR experiments and quadrupolar parameter ab initio calculations: Crystallographic structure refinement of ß-Ba3AlF9

M. Body, G. Silly, C. Legein, J.-Y. Buzaré, F. Calvayrac and P. Blaha

aLaboratoire de Physique de l’Etat Condensé, CNRS UMR 6087, Institut de Recherche en Ingénierie Moléculaire et Matériaux Fonctionnels, CNRS FR 2575, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France
bLaboratoire des Oxydes et Fluorures, CNRS UMR 6010, Institut de Recherche en Ingénierie Moléculaire et Matériaux Fonctionnels, CNRS FR 2575, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France
cLaboratoire de Physicochimie de la Matière Condensée, CNRS UMR 5617, Institut Charles Gerhardt, CNRS FR 1878, Université de Montpellier II, Place Eugène Bataillon, C.C. 03, 34095 Montpellier Cedex 5, France
dInstitute of Materials Chemistry, Vienna University of Technology A-1060 Vienna, Getreidemarkt 9/165-TC, Austria

Abstract

27Al quadrupolar parameters are determined for the three aluminium sites in ß-Ba3AlF9 from the reconstruction of experimental SATRAS and MQ-MAS NMR spectra. These quadrupolar parameters are then computed using the DFT linearized augmented plane wave method implemented in the WIEN2k code.

A fine agreement between experimental and calculated values is obtained only after optimizing the ß-Ba3AlF9 structure. The optimized structure is more satisfactory than the previously published one from a crystallographic point of view (bond lengths and angles).

This approach which allows to refine crystallographic structures especially when they lack accuracy may be extendable to other compounds containing quadrupolar nuclei.

Hiyam's Journal Updates

Quadrupolar coupling selective cross-polarization in solid state NMR
Physical Chemistry Chemical Physics, 2006, 8, 1994 - 1999

Mattias Edén

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A new strategy is presented for achieving selective heteronuclear polarization transfers from half-integer quadrupolar spins in magic-angle spinning (MAS) NMR. By combining cross-polarization with a recently introduced RAPT pulse sequence that selectively excites the signal of a half-integer quadrupolar nucleus based on its quadrupolar coupling constant magnitude, we demonstrate that hetero-nuclei in its close proximity may be selectively excited. Selective ²³Na ¹H polarization transfers are demonstrated in Na₂MoO₄·2H₂O, Na₂HPO₄·2H₂O and a mixture of NaHCO₃ and Na₂HPO₄·2H₂O.

Medium-range order in sodium phosphate glasses: A quantitative rotational echo double resonance solid state NMR study
Physical Chemistry Chemical Physics, 2006, 8, 2276 - 2285

Wenzel Strojek and Hellmut Eckert

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Sodium ultraphosphate glasses (Na₂O)_x(P₂O₅)_1–x show a strongly non-linear dependence of the glass transition temperatures T_g(x) on composition. To explore the structural origins of this behaviour, local and medium range ordering processes have been investigated by state-of-the-art ²³Na high-resolution and dipolar NMR spectroscopies. In particular, ³¹P{²³Na} and ²³Na{³¹P} rotational echo double resonance (REDOR) experiments have been analyzed to yield quantitative constraints for the structural description of these glasses. The sodium ions are found to be randomly distributed and, for x <>⁽²⁾ unit at a distance of 330 pm. In this region, unusual compositional trends observed for the ²³Na chemical shifts and nuclear electric quadrupolar coupling constants, measured by triple-quantum magic-angle spinning (TQMAS) NMR, suggest a systematic decrease of Na coordination number with x. At higher sodium contents (x > 0.25), the magnitude of the ³¹P{²³Na} dipolar interaction increases markedly, indicating a significantly increased extent of Q⁽²⁾-Na-Q⁽²⁾ crosslinking. Based on these results, a comprehensive description of medium-range order in sodium ultraphosphate glasses is developed, suggesting that the T_g(x) dependence is closely linked to changes in the relative phosphorus/sodium distance distributions.

Acid sites and oxidation center in molybdena supported on tin oxide as studied by solid-state NMR spectroscopy and theoretical calculation
Physical Chemistry Chemical Physics, 2006, 8, 2378 - 2384

Jiqing Wang, Yongchao Su, Jun Xu, Chaohui Ye and Feng Deng

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Solid-state NMR spectroscopy and density functional theory (DFT) calculations were employed to study the structure and properties, especially the solid acidity, of molybdenum oxide supported on tin oxide. As demonstrated by solid-state NMR experiments, Mo species are mainly dispersed on the surface of SnO₂ support rather than significantly dissolved into the SnO₂ structure and Brønsted as well as Lewis acid sites are present on the MoO₃/SnO₂ catalyst. Acid strength of the supported metal oxide is stronger than those of zeolites, e.g., HY and HZSM-5, though the concentration of acid sites is relatively lower. The DFT calculated ¹³C chemical shift for acetone adsorbed on MoO₃/SnO₂ is in good agreement with the experimental value, which confirms our proposed structure of –Mo–(OH)–Sn– for the Brønsted acid site. Reducibility of the supported metal oxide is also demonstrated by solid-state NMR experiments and an active oxidation center of this catalyst is proposed as well.

JPCB: Francesconi and Polenova, 31P of paramagnetic Keggin solids

Probing Local Environments in Paramagnetic Europium-Substituted Keggin Solids by 31P Magic Angle Spinning NMR Spectroscopy

Wenlin Huang, Mark Schopfer, Cheng Zhang, Robertha C. Howell, Becky A. Gee, Lynn C. Francesconi,* and Tatyana Polenova*

Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, Department of Chemistry, City University of New York-Hunter College, 695 Park Avenue, New York, New York 10021, and Department of Chemistry and Biochemistry, Long Island University-Brooklyn Campus, 1 University Plaza, Brooklyn, New York 11201

Abstract:

Paramagnetic Eu-substituted Keggin oxopolytungstates crystallize in different forms, determined by the nature of the counterions. The crystal packing is in turn responsible for the variations in the geometry of paramagnetic Eu sites with respect to the anion core. We probed the paramagnetic environments in a series of Eu-substituted Keggin solids, by 31P magic angle spinning NMR spectroscopy. 31P spinning sideband envelopes are dominated by the electron-nuclear dipolar interaction. For the compounds under investigation, both the magnitude and the asymmetry parameter of the electron-nuclear dipolar coupling tensor are sensitive to the mutual arrangements of paramagnetic Eu sites in the crystal lattice. and also report on the stoichiometry of the anion. The electron-nuclear dipolar coupling tensors were calculated from the crystallographic coordinates and the experimentally determined effective magnetic moments, assuming a point dipole approximation. The computed tensors are in very good agreement with the experimental spectra. Furthermore, the P-Eu distance estimates, accurate to within 0.06-0.12 Å, can be obtained directly from the magnitude of the electron-nuclear dipolar coupling. This work demonstrates that 31P MAS NMR spectroscopy is a useful probe for investigating local environments in paramagnetic Keggin solids.

PCCP: high pressure 129Xe NMR to probe effects of pressure and density

Phys. Chem. Chem. Phys., 2006, (Advance Article)
DOI: 10.1039/b604633a

Local structure of xenon adsorbed in the nanospaces of zeolites as studied by high-pressure 129Xe NMR

Hironori Omi, Takahiro Ueda, Noriko Kato, Keisuke Miyakubo and Taro Eguchia

aDepartment of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan

bThe Museum of Osaka University, Toyonaka, Osaka, 560-0043, Japan. E-mail: ueda@museum.osaka-u.ac.jp; Fax: +81-6-6850-5785; Tel: +81-6-6850-5778
Received (in CAMBS) 30th March 2006, Accepted 30th May 2006

Pressure (0–10 MPa) and local density dependence of 129Xe NMR chemical shift of xenon in various microporous materials was investigated using an in situ high-pressure probe. The density dependence of the chemical shift was analyzed using virial expansion of the chemical shift by xenon density. Results indicate that the second virial coefficient depends on the pore size and shape, and that the void space affects xenon–xenon interaction in both microporous and mesoporous materials. Furthermore, to interpret the magnitude of the virial coefficient in terms of the local structure of the adsorbed xenon, we analyzed the local structure of adsorbed xenon in molecular sieve 5A using Xen clusters, thereby allowing description of the density dependence of the chemical shift. We also demonstrated the cluster models validity by applying it to molecular sieves 13X and ZSM-5. The latter showed that the adsorbed xenon exists as a xenon monomer up to the filling of about 0.6 in micropores. Larger xenon clusters up to n= 4 have been grown with increasing filling of xenon. According to analyses using the Xen cluster model, the second virial coefficient is related closely with the xenon cluster size, which contributes greatly to the chemical shift in the low loading region.

JPCA, de Dios, CS tensoirs in 4-aminoquinolines; heme-drug interactions

J. Phys. Chem. A, ASAP Article 10.1021/jp061320t S1089-5639(06)01320-X
Web Release Date: June 6, 2006

Relationship between NMR Shielding and Heme Binding Strength for a Series of 7-Substituted Quinolines

Leah B. Casabianca and Angel C. de Dios*

Department of Chemistry, Georgetown University, 37th and O Streets NW, Washington, DC 20057

Abstract:

Chemical shielding tensors are calculated for the carbons in a series of 4-aminoquinolines with different substituents at the 7-position. The 11 component is used as a measure of the relative -electron density at each carbon. By comparing the -electron density at each carbon with the log K of binding to heme (Kaschula et al. J. Med. Chem. 2002, 45, 3531), the drug-heme association is found to increase with increasing -electron density at the carbons meta to the substituent and with decreasing -electron density at the carbons ortho and para to the substituent. The greatest change in -electron density is at the ortho carbons, and log K increases with a decrease in -electron density on the ring containing the substituent, which corresponds to an increase in the -dipole between the two rings. An examination of the solution structures of the - complexes formed by amodiaquine and quinine with heme (Leed et al. Biochemistry 2002, 41, 10245. de Dios et al. Inorg. Chem. 2004, 43, 8078) shows that the -dipoles in each drug and in the porphyrin ring of heme may be paired. The chloro-substituted compound has an association constant that is an order of magnitude higher than the other compounds in the series, but the -electron density at the ring containing the substituent is not correspondingly low. This lack of correlation indicates that the Cl-substituted compound may be binding to heme in a manner that differs from the other compounds in the series.

JPCB: Stebbins and Du, 17O, 23Na NMR of Na germanate glasses

J. Phys. Chem., ASAP Article 10.1021/jp0615510 S1520-6106(06)01551-3
Web Release Date: June 3, 2006

Oxygen Sites and Network Coordination in Sodium Germanate Glasses and Crystals: High-Resolution Oxygen-17 and Sodium-23 NMR

Lin-Shu Du and Jonathan F. Stebbins*

Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115

Abstract:

Sodium germanate glasses are well-studied materials in which, unlike silicates but analogous to borates, the major structural consequence of alkali addition is generally thought to involve a coordination number increase of the network-forming Ge cations. However, the nature of this change, in particular quantifying fractions of nonbridging oxygens and of five- and/or six-coordinated Ge, has remained unresolved. We present here high-resolution 17O results, including triple-quantum MAS NMR (3QMAS), on a series of crystalline model compounds that allow the definition of ranges of chemical shifts corresponding to oxygens bonded to various coordinations of Ge. These include quartz- and rutile-structured GeO2, Na4Ge9O20, Na2Ge4O9, and Na2GeO3 (germanium dioxide, sodium enneagermanate, sodium tetragermanate, and sodium metagermanate). 3QMAS spectra of Na-germanate glasses ranging from 0% to 27% Na2O clearly show the development of partially resolved peaks as alkali is added, corresponding to signals from nonbridging oxygens (in the highest Na glasses) and to oxygen bridging between one four-coordinated and one higher coordinated Ge. As in conventional models of this system, nonbridging oxygen contents are much lower than in corresponding silicates. Although we do not directly distinguish between five- and six-coordinated Ge, modeling of bridging oxygen populations and comparison with measured speciation suggest that substantial proportions of both species are likely to be present. High-field 23Na MAS NMR shows systematic decreases in mean Na-O bond distance and/or coordination number with increasing alkali content that can be compared with published results for high-temperature liquids. These results, as well as comparison of molar volumes of glasses and high-temperature liquids, suggest the possibility of significant temperature effects on liquid structure.

JACS, Bodenhausen, indirect detection of 14N spectra via residual dipolar coupling - similar to Gan's work?

J. Am. Chem. Soc., ASAP Article 10.1021/ja0618898 S0002-7863(06)01889-0
Web Release Date: May 26, 2006

Nitrogen-14 NMR Spectroscopy Using Residual Dipolar Splittings in Solids

Simone Cavadini, Adonis Lupulescu, Sasa Antonijevic,* and Geoffrey Bodenhausen

Laboratoire de Résonance Magnétique Biomoléculaire, Ecole Polytechnique Fédérale de Lausanne, Batochime, CH-1015 Lausanne, Switzerland, and Département de Chimie, associé au CNRS, Ecole Normale Supérieure, 24 rue Lhomond 75231, Paris Cedex 05, France

Abstract:

It is shown that nuclear magnetic resonance (NMR) spectra of nitrogen-14 (spin I = 1) can be obtained by indirect detection in powders spinning at the magic angle (MAS). The method relies on the transfer of coherence from a neighboring nucleus with S = 1/2, such as carbon-13, to single- or double-quantum transitions of nitrogen-14 nuclei. The transfer of coherence occurs through second-order quadrupole-dipole cross terms, also known as residual dipolar splittings. The two-dimensional NMR spectra reveal powder patterns determined by the second-order quadrupolar interactions of nitrogen-14. Analysis of the spectra yields the quadrupolar coupling.

JACS, Mark Smith et al, 17O NMR applied to biological molecules; DOR applications

J. Am. Chem. Soc., ASAP Article 10.1021/ja062031l S0002-7863(06)02031-2
Web Release Date: May 26, 2006

New Limits for Solid-State 17O NMR Spectroscopy: Complete Resolution of Multiple Oxygen Sites in a Simple Biomolecule

Alan Wong, Andy P. Howes, Kevin J. Pike, Vincent Lemaître, Anthony Watts, Tiit Anupõld, Jaan Past, Ago Samoson, Ray Dupree,* and Mark E. Smith*

Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom, Biochemistry Department, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom, and National Institute for Chemical Physics and Biophysics, Akadeemia Tee 23, Tallinn, Estonia

Abstract:

A solid-state 17O NMR 1H-decoupled double angle rotation (DOR) study of monosodium L-glutamate monohydrate (L-MSG) is reported. It is shown that all eight inequivalent sites can be resolved with DOR line widths (~65 Hz) ~120 times narrower than those in the MAS spectrum. The lines are tentatively assigned on the basis of their behavior under proton decoupling and the isotropic chemical shift and the quadrupole interaction parameter for each extracted by a combination of DOR and 3Q MAS at variable magnetic fields. With a shift range of ~45 ppm for these similar oxygen sites and spectral resolution under DOR comparable to that for spin-1/2 nuclei, solid-state 17O NMR should have tremendous potential in the study of biomolecules.

JACS: Wasylishen & Forgeron, 95MO NMR and DFT calculations

J. Am. Chem. Soc., ASAP Article 10.1021/ja060124x S0002-7863(06)00124-7
Web Release Date: May 25, 2006

A Solid-State 95Mo NMR and Computational Investigation of Dodecahedral and Square Antiprismatic Octacyanomolybdate(IV) Anions: Is the Point-Charge Approximation an Accurate Probe of Local Symmetry?

Michelle A. M. Forgeron and Roderick E. Wasylishen*

Contribution from the Department of Chemistry, Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2G2

Abstract:

Solid-state 95Mo NMR spectroscopy is shown to be an efficient and effective tool for analyzing the diamagnetic octacyanomolybdate(IV) anions, Mo(CN)84-, of approximate dodecahedral, D2d, and square antiprismatic, D4d, symmetry. The sensitivity of the Mo magnetic shielding () and electric field gradient (EFG) tensors to small changes in the local structure of these anions allows the approximate D2d and D4d Mo(CN)84- anions to be readily distinguished. The use of high applied magnetic fields, 11.75, 17.63 and 21.1 T, amplifies the overall sensitivity of the NMR experiment and enables more accurate characterization of the Mo and EFG tensors. Although the magnitudes of the Mo and EFG interactions are comparable for the D2d and D4d Mo(CN)84- anions, the relative values and orientations of the principal components of the Mo and EFG tensors give rise to 95Mo NMR line shapes that are significantly different at the fields utilized here. Quantum chemical calculations of the Mo and EFG tensors, using zeroth-order regular approximation density functional theory (ZORA DFT) and restricted Hartree-Fock (RHF) methods, have also been carried out and are in good agreement with experiment. The most significant and surprising result from the DFT and RHF calculations is a significant EFG at Mo for an isolated Mo(CN)84- anion possessing an ideal square antiprismatic structure; this is contrary to the point-charge approximation, PCA, which predicts a zero EFG at Mo for this structure.

Cory's Journals - May 2006

May 2006 articles from the journals that I am responsible for will be placed in their usual folder by the end of today.