Tuesday, July 20, 2010

J. Phys. Chem C. v. 114, issue 28

45Sc Spectroscopy of Solids: Interpretation of Quadrupole Interaction Parameters and Chemical Shifts

Mara D. Alba*†, Pablo Chain†, Pierre Florian‡ and Dominique Massiot‡

J. Phys. Chem. C, 2010, 114 (28), pp 12125–12132
Publication Date (Web): June 28, 2010

Abstract: The aims of the present study is to describe for the first time the 45Sc MAS NMR spectra of X2-Sc2SiO5 and C-Sc2Si2O7, to combine the spectroscopic information with the structures published from diffraction data, and to propose a rational interpretation of the chemical shifts and quadrupolar parameters. For that purposed, we have correlated the experimental quadrupole coupling parameters of 45Sc determined for a number of scandium compounds to those found by a simple electrostatic calculation and we have found that the isotropic chemical shift of the 45Sc is linearly correlated to the shift parameter, calculated by bond-valence theory. We also show that a simple point charge calculation can approximate the electric field gradient to a sufficiently good approximation that it provides a valuable mean to assign the NMR spectra.

Nuclear Magnetic Resonance Study of Reorientational Motion in α-Mg(BH4)2
Alexander V. Skripov*†, Alexei V. Soloninin†, Olga A. Babanova†, Hans Hagemann‡ and Yaroslav Filinchuk§
J. Phys. Chem. C, 2010, 114 (28), pp 12370–12374
Copyright © 2010 American Chemical Society

Abstract: To study the reorientational motion of BH4 groups in the low-temperature (α) phase of Mg(BH4)2, we have performed nuclear magnetic resonance (NMR) measurements of the 1H and 11B spin−lattice relaxation rates in this compound over wide ranges of temperature (82−443 K) and resonance frequency (14−90 MHz for 1H and 14−28 MHz for 11B). It is found that the thermally activated reorientational motion in α-Mg(BH4)2 is characterized by a coexistence of at least three jump processes with strongly differing activation energies. Taking into account the anisotropy of the local environment of BH4 groups in α-Mg(BH4)2, these jump processes can be attributed to different types of reorientation. The nearly linear coordination of BH4 groups by two Mg atoms suggests that the fastest jump process corresponds to the rotation around the 2-fold axis connecting B and two Mg atoms, whereas the slowest process is associated with the rotation around two other 2-fold axes perpendicular to the Mg−B−Mg line.

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