Electron spin echo modulation studies of tetracyanoethylene anion solvation in methanol, acetone, and dimethylsulfoxide: Evidence for molecular dipole oriented solvation shells around large anions

Electron spin echo modulation studies have been carried out for the tetracyanoethylene anion (TCNE−) in CD3OH, CH3OD, (CD3)2CO, and (CD3)2SO at 4.2 K to deduce details of the anion solvation geometry in these solvents. The deuterium modulation patterns have been analyzed using ratio analysis and complete simulation. The results indicate that TCNE− is solvated by four methanol molecules with the methanol molecular dipole oriented toward the anion; the distances from the anion to the hydroxyl and methyl deuterons are 5.9 and 3.8 Å, respectively. TCNE− is solvated by two molecules of acetone or dimethylsulfoxide; it is suggested that these solvating molecules are above and below the TCNE− plane with their molecular dipoles oriented toward the C=C bond in TCNE−. The anion–deuteron distances are 4.2 Å in acetone and 3.6 Å in dimethylsulfoxide; the larger distance correlates with the smaller of the molecular dipole moments which are 2.6 and 4.0 D, respectively.