Solvation of GaCl3 in deuterated acetonitrile studied by means of vibrational spectroscopy.

Remarkably large blue shifts of the nu2 C [triple bond] N stretch, nu4 C-C stretch, and nu8 CCN deformation bands of CD3CN are observed in the infrared and Raman spectra of CD3CN solution of GaCl3, resulting from the donor-acceptor interaction of CD3CN with the Lewis acid. The Raman spectrum in the nu2 region shows further details; three new bands emerge on the blue side of the nu2 band of free CD3CN and the relative intensities between the bands vary with concentration, suggesting that there exist at least three different complexes in the solution. Parallel to the nu2 region, similar new bands are observed on the blue sides of the nu4 and nu8 bands of free CD3CN. The strong hydrogen bonds formed between the CD3 group and the chlorine atoms of the solute result in a large band appearing on the low frequency side of the nu1 CD3 symmetric stretch band of free CD3CN. The solvation number of GaCl3, as determined from the Raman intensities of the C [triple bond] N stretch bands for free and coordinated CD3CN, increases from 1.3 to about 1.7 with decreasing concentration.