ABSTRACT
Large blue shifts of the nu2 C=N stretch, nu4 Cz.sbnd;C stretch, and nu8 CCN deformation bands of CD3CN are observed in the infrared and Raman spectra of CD3CN solution of AlCl3, resulting from the donor-acceptor interactions of CD3CN with the Lewis acid. The Raman spectrum in the nu2 region shows further details; two new bands emerge on the blue side of the nu2 band of free CD3CN, and the ratio in intensity of the two bands also changes with concentration. Parallel to the nu2 region, similar new bands are observed on the blue sides of the nu4 and nu8 bands of free CD3CN. The solvation number of AlCl3, determined from the Raman intensities of the C=N stretch bands for free and coordinated CD3CN, increases from 1.54 to about 1.7 with decreasing concentration, indicating that various complexes with different numbers of coordinated acetonitrile coexist in the solution. 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 of free CD3CN.
Subject(s)
Aluminum Compounds/chemistry , Chlorides/chemistry , Acetonitriles , Aluminum Chloride , Deuterium , Hydrogen Bonding , Solvents , Spectroscopy, Fourier Transform Infrared , Spectrum Analysis, RamanABSTRACT
Vibrational characteristics of CD3CN solutions of LiClO4 and NaClO4 have been studied by means of infrared and Raman spectroscopy. Blue shifts of 22 and 11 cm(-1) of the v2 C[triple bond]N stretch are observed resulting from interaction of CD3CN with Li+ and Na+, respectively. The number of primary solvation sites of both Li+ and Na+ in acetonitrile is believed to be four from the comparison of the Raman intensities of the C[triple bond]N stretch for free CD3CN and those coordinated to Li+ and Na+. Evidently formation of contact ion pairs of the cation (Li+ or Na+) and anion (ClO4-) is more probable at a higher concentration of the salt. The characteristics of the v2 C[triple bond]N stretch, v4 C-C stretch, and v8 CCN deformation bands vary substantially upon coordination, while other vibrational bands are relatively immune to the donor-acceptor interaction. DFT calculations have also been performed at the BLYP/6-31 + G(2d,p) level to examine the structures and vibrational characteristics of CD3CN coordinated to Li+ and Na+. The calculated results are in good agreement with the observed vibrational characteristics.
