Interactions between metal complex ions and water. Part 1.—Partial molal volumes, viscosity coefficients and conductivities of trivalent CoIII and CrIII complex ions in water

Abstract

The apparent molal volumes, viscosity coefficients and conductivities of [ML6]X3[M = CoIII or CrIII, L = NH3, H2O, ethylenediamine/2(= en/2), 1,3-diaminopropane/2(= tn/2), biguanide/2(= bgH/2) or urea, X = Cl– or NO–3] in water have been measured at 25 °C. The polarization charge densities at the surface of the metal complex ions, σp, were obtained from the ionic partial molal volumes and the dipole moments of the ligands. The difference between the viscosity Bη coefficient and the ionic partial molal volume or between the Stokes' radius and the radius calculated from the ionic partial molal volume is a function of σp. We suggest that the complex ions change from hydrophobic structure-makers to hydrophobic structure-breakers as σp increases from 0 to the σp of [Cr(urea)6]3+, followed by another change from electrostrictive structure-breakers to electrostrictive structure-makers as σp increases from the σp of [Cr(urea)6]3+, which is the transition point between hydrophobic and electrostrictive ions.