Solvation of Mg(ClO4)(2) in deuterated acetonitrile studied by means of vibrational spectroscopy

Vibrational characteristics of CD3CN solution containing Mg(ClO4)(2) have b een studied by means of infrared and Raman spectroscopy. A large blue shift of 40 cm(-1) and a relatively small red shift of 3 cm(-1) of the v(2) C eq uivalent toN stretch are observed as a result of interactions of CD3CN with Mg2+ and ClO4- ions, respectively. The Mg2+ ion is preferentially solvated by residual water over acetonitrile. The primary coordination number of Mg 2+ in acetonitrile is determined as 6 from the Raman intensities of the C d ropN stretch for free CD3CN and those coordinated to Mg2+. Evidently, forma tion of contact ion pairs of Mg2+ and ClO4- is more probable at a high conc entration of Mg(ClO4)(2). The IR extinction constants of the v(2) and v(4) stretching bands increase dramatically upon coordination. The vibrational c haracteristics of free CD3CN remain the same in the solution, indicating th at the electrophilicity of Mg2+ affects only the CD3CN molecules directly c oordinated to Mg2+. DFT calculations have been performed at the BLYP/6-31+G (2d,p) level to examine the structure and vibrational characteristics of CD 3CN coordinated to Mg2+. The calculated results are in good agreement with the observed vibrational characteristics.