Thursday, August 09, 2007

Solid-State NMR, Vol. 32, August 2007

Solid-State NMR, Vol. 32, August 2007

Using liquid and solid state NMR and photoluminescence to study the synthesis and solubility properties of amine capped silicon nanoparticles

J.R. Giuliani1, a, S.J. Harleya, R.S. Cartera, P.P. Powera and M.P. Augustine
Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA
Received 12 December 2006. Available online 29 May 2007.


Water soluble silicon nanoparticles were prepared by the reaction of bromine terminated silicon nanoparticles with 3-(dimethylamino)propyl lithium and characterized with liquid and solid state nuclear magnetic resonance (NMR) and photoluminescence (PL) spectroscopies. The surface site dependent 29Si chemical shifts and the nuclear spin relaxation rates from an assortment of 1H–29Si heteronuclear solid state NMR experiments for the amine coated reaction product are consistent with both the 1H and 13C liquid state NMR results and routine transmission electron microscopy, ultra-violet/visible, and Fourier transform infrared measurements. PL was used to demonstrate the pH dependent solubility properties of the amine passivated silicon nanoparticles.

Keywords: Nanoparticles; 29Si nuclear magnetic resonance; Nuclear spin relaxation; Photoluminescence

A computational investigation of 17O quadrupolar coupling parameters and structure in α-quartz phase GeO2

Travis H. Sefzika, Ted M. Clarka and Philip J. Grandinetti
aDepartment of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Received 12 March 2007; revised 4 June 2007. Available online 10 July 2007.


Ab initio band-structure calculations based on density functional theory have been completed for α-quartz phase GeO2 to obtain electric-field gradients (efg) for oxygen atoms, including those for GeO2 at elevated pressure and temperature. To interpret the resulting efg values and examine correlations between structure and 17O quadrupolar coupling parameters, additional ab initio self-consistent Hartree-Fock molecular orbital calculations were completed. The quadrupolar coupling constant was found to have a strong dependence on Ge–O distance and angleGe–O–Ge, with the quadrupolar asymmetry parameter being primarily dependent on angleGe–O–Ge. Analytical expressions describing these dependencies consistent with earlier investigations of analogous silicate compounds are also reported.

Study of molecular reorientation and quantum rotational tunneling in tetramethylammonium selenate by 1H NMR

K.J. Mallikarjunaiah a, K.C. Paramita b, K.P. Ramesh b and R. Damle a
aDepartment of Physics, Bangalore University, Bangalore 560 056, India
bDepartment of Physics, Indian Institute of Science, Bangalore 560 012, India
Received 27 April 2007. Available online 10 July 2007.


1H NMR spin–lattice relaxation time measurements have been carried out in [(CH3)4N]2SeO4 in the temperature range 389–6.6 K to understand the possible phase transitions, internal motions and quantum rotational tunneling. A broad T1 minimum observed around 280 K is attributed to the simultaneous motions of CH3 and (CH3)4N groups. Magnetization recovery is found to be stretched exponential below 72 K with varying stretched exponent. Low-temperature T1 behavior is interpreted in terms of methyl groups undergoing quantum rotational tunneling.

Keywords: 1H NMR; Internal motions; Magnetization recovery; Spin–lattice relaxation time; Quantum rotational tunneling

No comments: