The importance of preferential solvation of the CN ligands in electron- and proton-transfers observed for cis–[Ru(CN)2(bpy)2] under ion bombardment

Liquid secondary ion mass spectrometry (LSIMS) mass spectra of cis-[Ru(CN)2(bpy)2] with a strong hydrogen-bonding-induced solvatochromism were measured using 3-nitrobenzyl alcohol (NBA) (oxidizing agent) and glycerol (reducing agent), and mixtures of these solvents. The formation of M+ (oxidized molecule) correlated closely to the extent of preferential solvation by NBA (preferential solvation-shell) around the cyanide ligands as observed from changes in the energy of the maximum metal-to-ligand charge transfer absorption. (M + H)+ is caused mainly by the preferential orientation of OH groups with protons in the NBA molecules toward the cyanide ligands in the disrupted region of the solvent structure as observed from the variation in the peak position of the stretching vibration of (OH) in the solvents. Large decreases in (M + 2H)+ and (M + 3H)+ (reduced molecules) resulted from the large decrease in the interaction between the cyanide ligands and glycerol owing to the preferential solvation by NBA. The LSIMS mass spectra clearly showed the electron- and proton-transfer processes along with the change in the hydrogen-bonding interaction between the acceptor (NBA and glycerol) and donor (the cyanide ligands), and in the solvent structure of the preferential solvation-shell. These results indicate that the composition of solvent molecules around the cyanide ligands at the surface of the solvents in LSIMS still holds the composition in the preferential solvation around the ligands in the primary solvation-shell.