Spectroscopic studies of ionic solvation. XXI. A raman,infrared, and NMR study of sodium perchlorate solutions in nonaqueous solvents

Sodium perchlorate solutions in several nonaqueous solvents were examined by²³Na,³⁵Cl-NMR, infrared, and Raman spectroscopic techniques. The formation of contact ion pairs lowers the symmetry of ClO₄^– ion from T_d to C_3v or C_2v provided that the interaction is fairly strong. This was manifested for NaClO₄ solutions in acetonitrile, tetrahydrofuran, and pyridine. Combination of the vibrational measurements with NMR shows that in the above three cases the anion-cation interactions are quite strong. Sodium-23 NMR studies confirm the above results and, being a more sensitive technique, also indicates weak cation-anion interaction in propylene carbonate, formic acid, acetone, methanol, ethanol, dimethyl sulfoxide, and water. In all solvents the²³Na resonance shifts upfield with increasing concentration of NaClO₄, indicating that the replacement of solvent by ClO₄^– ion decreases electron density around the cation.