Monday, December 19, 2005

Latest online articles: Dec 19/05

December 19, 2005 - New articles

Cory, interesting 31P NMR
Chemical Communications, 2005, (Advance Article)
DOI: 10.1039/b513037a
No aromaticity of P64– observed via solid state 31P-NMR spectroscopy
Florian Kraus, Jörn Schmedt auf der Günne, Brian F. DiSalle and Nikolaus Korber
The solid state NMR spectra of the binary alkali hexaphosphides Rb4P6 and Cs4P6 unambiguously show the P64– anion not to be aromatic.

6Li NMR, spin-1 nuclei

Chem. Mater., ASAP Article 10.1021/cm0508773 S0897-4756(05)00877-X
Web Release Date: November 22, 2005

6Li NMR Studies of Cation Disorder and Transition Metal Ordering in Li[Ni1/3Mn1/3Co1/3]O2 Using Ultrafast Magic Angle Spinning

L. S. Cahill, S.-C. Yin, A. Samoson, I. Heinmaa, L. F. Nazar, and G. R. Goward*

Revised Manuscript Received October 13, 2005


Studies of Li[Ni1/3Mn1/3Co1/3]O2 prepared under six different conditions are compared using high-resolution solid-state 6Li NMR. Differing degrees of cation disorder are established via integration of the NMR resonances, and this quantification of cation disorder is compared with Rietveld refinements of powder X-ray and neutron diffraction studies. Chemical shift trends to high frequency with decreasing degrees of disorder are established among this family of samples and explained according to the orbital overlap experienced by Li nuclei in the two environments: within the lithium layers and exchanged with nickel into the transition metal layers. Finally, an interesting case of local transition metal charge ordering is observed. Three unique environments are described, which can be accounted for based on electroneutrality arguments, and the known clustering of Ni2+ and Mn4+. This effect has not been detected in these materials by other methods including neutron and X-ray diffraction. Thus, the local ordering, which is observed in the dominant NMR resonance of Li in its own layers is thought to be pervasive (affecting the majority of the NMR nuclei), but very local, so as to be seen only by techniques such as NMR which probe immediate neighborhoods.

Cory, 31P NMR
J. Phys. Chem. A, ASAP Article 10.1021/jp0555910 S1089-5639(05)05591-X
Web Release Date: December 3, 2005

A Theoretical Study of 31P NMR Chemical Shielding Models for Concentrated Phosphoric Acid Solution
D. B. Chesnut
P. M. Gross Chemical Laboratory, Duke University, Durham, North Carolina 27708
In Final Form: November 5, 2005

Calculations on the hydrates, dimer, and trimer of phosphoric acid were carried out in an effort to obtain a viable model of the phosphorus NMR chemical shielding in 85% phosphoric acid solution. The theoretical approaches used the gauge-including-atomic-orbital (GIAO) 6-311+G(nd,p) basis set at both scaled density functional theory (sB3LYP) and estimated infinite order Mller-Plesset (EMPI) approaches and with the aug-cc-pvtz basis in the sB3LYP approach. Shieldings and hydrogen bonding stabilization energies are similar in the three approaches and indicate that the faster sB3LYP/6-311+G(nd,p) approach can be used with larger systems. The changes in shielding compared to the isolated species are small and suggest that the undissociated acid dihydrate could serve as a model entity for modeling the phosphorus shielding in concentrated phosphoric acid solution.

Andy, Joel

J. Phys. Chem. B, ASAP Article 10.1021/jp055130e S1089-5647(05)05130-8
Web Release Date: December 14, 2005

Dynamics of p-Nitroaniline Molecules in Micoporous Aluminophosphate AlPO4-5 Studied by Solid-State NMR
Yoshihiko Komori and Shigenobu Hayashi*

Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

In Final Form: November 7, 2005


Dynamics of deuterated p-nitroaniline (pNA-d) molecules in the micropores of AlPO4-5 has been investigated by means of solid-state NMR. The adsorbed amounts of pNA-d were 5.0 and 10.1 mass % of the total mass. We have measured 13C magic-angle-spinning (MAS) and 2H NMR spectra of the guest molecules and 31P and 27Al MAS NMR spectra of the host framework. The pNA-d molecules distribute rather inhomogeneously in the channel, and do not coordinate to Al strongly like H2O. The intermolecular hydrogen bonds are formed between a part of the guest molecules only when the loading level is high. The 2H NMR spectra are successfully analyzed, elucidating the orientation and the motion of the guest molecules. The molecular axis of pNA-d is inclined to the channel axis, and the molecular plane is perpendicular to the inner wall. The guest molecule jumps among 12 sites or 12 orientations. This motion is faster in the sample of 5.0 mass % than in the sample of 10.1 mass %, suggesting that the guest-guest interaction hinders the motion. The mean residence times of the molecules are estimated from the analysis of the 2H NMR spectra, which are affected by the size of the nanospace as well as the property of the adsorbed site.

J. Phys. Chem. B, ASAP Article 10.1021/jp054022p S1089-5647(05)04022-8
Web Release Date: December 15, 2005

31P NMR Chemical Shifts in Hypervalent Oxyphosphoranes and Polymeric Orthophosphates
Yong Zhang and Eric Oldfield*

Departments of Chemistry and Biophysics, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801

In Final Form: November 14, 2005


We report the first quantum chemical investigation of the solid- and solution-state 31P NMR chemical shifts in models for phosphoryl transfer enzyme reaction intermediates and in polymeric inorganic phosphates. The 31P NMR chemical shifts of five- and six-coordinate oxyphosphoranes containing a variety of substitutions at phosphorus, as well as four-coordinate polymeric orthophosphates and four-coordinate phosphonates, are predicted with a slope of 1.00 and an R2 = 0.993 (N = 34), corresponding to a 3.8 ppm (or 2.1%) error over the entire 178.3 ppm experimental chemical shift range, using Hartree-Fock methods. For the oxyphosphoranes, we used either experimental crystallographic structures or, when these were not available, fully geometry optimized molecular structures. For the four-coordinate phosphonates we used X-ray structures together with charge field perturbation, to represent lattice interactions. For the three-dimensional orthophosphates (BPO4, AlPO4, GaPO4), we again used X-ray structures, but for these inorganic systems we employed a self-consistent charge field perturbation approach on large clusters, to deduce peripheral atom charges. For pentaoxyphosphoranes, the solvent effect on 31P NMR chemical shieldings was found to be very small (<0.5 r2 =" 0.923)">

Cory, others doing EFG calculations

J. Phys. Chem. A, ASAP Article 10.1021/jp0554947 S1089-5639(05)05494-0
Web Release Date: December 17, 2005

Influence of N-H???O and C-H???O Hydrogen Bonds on the 17O NMR Tensors in Crystalline Uracil: Computational Study

Ramsey Ida, Maurice De Clerk, and Gang Wu*

Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6

In Final Form: November 14, 2005

We report a computational study for the 17O NMR tensors (electric field gradient and chemical shielding tensors) in crystalline uracil. We found that N-H???O and C-H???O hydrogen bonds around the uracil molecule in the crystal lattice have quite different influences on the 17O NMR tensors for the two C=O groups. The computed 17O NMR tensors on O4, which is involved in two strong N-H???O hydrogen bonds, show remarkable sensitivity toward the choice of cluster model, whereas the 17O NMR tensors on O2, which is involved in two weak C-H???O hydrogen bonds, show much smaller improvement when the cluster model includes the C-H???O hydrogen bonds. Our results demonstrate that it is important to have accurate hydrogen atom positions in the molecular models used for 17O NMR tensor calculations. In the absence of low-temperature neutron diffraction data, an effective way to generate reliable hydrogen atom positions in the molecular cluster model is to employ partial geometry optimization for hydrogen atom positions using a cluster model that includes all neighboring hydrogen-bonded molecules. Using an optimized seven-molecule model (a total of 84 atoms), we were able to reproduce the experimental 17O NMR tensors to a reasonably good degree of accuracy. However, we also found that the accuracy for the calculated 17O NMR tensors at O2 is not as good as that found for the corresponding tensors at O4. In particular, at the B3LYP/6-311++G(d,p) level of theory, the individual 17O chemical shielding tensor components differ by less than 10 and 30 ppm from the experimental values for O4 and O2, respectively. For the 17O quadrupole coupling constant, the calculated values differ by 0.30 and 0.87 MHz from the experimental values for O4 and O2, respectively.

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