Vibrational spectroscopic force field studies of dimethyl sulfoxide and hexakis(dimethyl sulfoxide)scandium(iii) iodide, and crystal and solution structure of the hexakis(dimethyl sulfoxide)scandium(iii) ion

Abstract

Hexakis(dimethyl sulfoxide)scandium(III) iodide, [Sc(OS(CH₃)₂)₆]I₃ contains centrosymmetric hexasolvated scandium(III) ions with an Sc–O bond distance of 2.069(3) Å. EXAFS spectra yield a mean Sc–O bond distance of 2.09(1) Å for solvated scandium(III) ions in dimethyl sulfoxide solution, consistent with six-coordination. Raman and infrared absorption spectra have been recorded, also of the deuterated compound, and analysed by means of normal coordinate methods, together with spectra of dimethyl sulfoxide. The effects on the vibrational spectra of the weak intermolecular C–H⋯O interactions and of the dipole–dipole interactions in liquid dimethyl sulfoxide have been evaluated, in particular for the S–O stretching mode. The strong Raman band at 1043.6 cm⁻¹ and the intense IR absorption at 1062.6 cm⁻¹ have been assigned as the S–O stretching frequencies of the dominating species in liquid dimethyl sulfoxide, evaluated as centrosymmetric dimers with antiparallel polar S–O groups. The shifts of vibrational frequencies and force constants for coordinated dimethyl sulfoxide ligands in hexasolvated trivalent metal ion complexes are discussed. Hexasolvated scandium(III) ions are found in dimethyl sulfoxide solution and in [Sc(OSMe₂)₆]I₃. The iodide ion–dipole attraction shifts the methyl group C–H stretching frequency for (S–)C–H⋯I⁻ more than for the intermolecular (S–)C–H⋯O interactions in liquid dimethyl sulfoxide.