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 = Co^III or Cr^III, 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, σ_p, were obtained from the ionic partial molal volumes and the dipole moments of the ligands. The difference between the viscosity B_η 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 σ_p. We suggest that the complex ions change from hydrophobic structure-makers to hydrophobic structure-breakers as σ_p increases from 0 to the σ_p of [Cr(urea)₆]³⁺, followed by another change from electrostrictive structure-breakers to electrostrictive structure-makers as σ_p increases from the σ_p of [Cr(urea)₆]³⁺, which is the transition point between hydrophobic and electrostrictive ions.