Experimental and theoretical studies of 45Sc NMR interactions in solids

Solid-state Sc-45 NMR spectroscopy, ab initio calculations, and X-ray crystallography are applied to examine the relationships between Sc-45 NMR interactions and molecular structure and symmetry. Solid-state Sc-45 (I = 7/2) magic-angle spinning (MAS) and static NMR spectra of powdered samples of Sc(acac)(3), Sc(TMHD)(3), Sc(NO3)(3)center dot 5H(2)O, Sc(OAc)(3), ScCl3 center dot 6H(2)O, ScCl3 center dot 3THF, and ScCp3 have been acquired. These systems provide a variety of scandium coordination environments yielding an array of distinct Sc-45 chemical shielding (CS) and electric field gradient (EFG) tensor parameters. Acquisition of spectra at two distinct magnetic fields allows for the first observations of scandium chemical shielding anisotropy (CSA). Sc-45 quadrupolar coupling constants (C-Q) range from 3.9 to 13.1 MHz and correlate directly with the symmetry of the scandium coordination environment. Single-crystal X-ray structures were determined for Sc(TMHD)(3), ScCl3 center dot 6H(2)O, and Sc(NO3)(3)center dot 5H(2)O to establish the hitherto unknown scandium coordination environments. A comprehensive series of ab initio calculations of EFG and CS tensor parameters are in excellent agreement with the observed parameters. Theoretically determined orientations of the NMR interaction tensors allow for correlations between NMR tensor characteristics and scandium environments. Solid-state Sc-45, C-13, and F-19 NMR experiments are also applied to characterize the structures of the microcrystalline Lewis acid catalyst Sc(OTf)(3) (for which the crystal structure is unknown) and a noncrystalline, microencapsulated, polystyrene-supported form of the compound.