Experimental and Theoretical Studies of ~(45)Sc NMR Interactions in Solids

摘要

Solid-state ~(45)Sc NMR spectroscopy,ab initio calculations,and X-ray crystallography are applied to examine the relationships between ~(45)Sc NMR interactions and molecular structure and symmetry.Solid-state ~(-45)Sc (/ = 7/2) magic-angle spinning (MAS) and static NMR spectra of powdered samples of Sc-(acac)_3,Sc(TMHD)_3,Sc(NO_3)_3 centre dot 5H_2O,Sc(OAc)_3,ScCI_3 centre dot 6H_2O,ScCI_3 centre dot 3THF,and ScCp_3 have been acquired.These systems provide a variety of scandium coordination environments yielding an array of distinct ~(45)Sc 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).~(45)Sc quadrupolar coupling constants (CQ) 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,ScCI_3 centre dot 6H_2O,and Sc(NO_3)_3 centre dot5H_2O 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 ~(45)Sc,~(13)C,and ~(19)F 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.