Partial Molar Volumes and Refractions of Cobalt(III) Complexes, Part 1: Homologous Series of Hexaaminecobalt(III) Complexes

Both the partial molar volumes (V∘_solute) and refractions (R∘_solute) of the solute at infinite dilution have been determined for a series of four octahedral N₆-coordinated cobalt(III) species with increasing ligand size (ammonia, ethylenediamine, sepulchrate, and 1,2-diaminocyclohexane). The experimental values for V∘ _solute are consistent with the relative sizes of the ligands but show larger values than those generated by computer modeling as the size of the cation increases. This suggests that the void space of the cation increases with the size of the cation. It is proposed that increasing hydrophobicity of the alkane ligand frameworks contributes to larger volumes.