X-Ray Diffraction Studies of the Structures of Hydrated Divalent Transition-Metal Ions in Aqueous Solution

Abstract

Abstract X-ray scattering measurements have been carried out for concentrated aqueous solutions of divalent transition-metal perchlorates of manganese(II) to zinc(II). The radial distribution curves showed that each central metal ion was octahedrally surrounded by six water molecules at the distances of 2.20 Å for Mn2+–OH2, 2.12 Å for Fe2+–OH2, 2.08 Å for Co2+–OH2, 2.04 Å for Ni2+–OH2, and 2.08 Å for Zn2+–OH2. The results from the radial distribution curves were confirmed by the direct analysis of reduced intensities. Concentrated aqueous solutions of copper(II) and zinc(II) sulfates have also been measured. The bond distances of 1.94 Å for the Cu2+–OH2 (equatorial), 2.38 Å for the Cu2+–OH2 (axial) and 2.08 Å for Zn2+–OH2 were consistent with those obtained for the perchlorate solutions. No evidence for the contact ion pairs of metal and sulfate ions was found by the present X-ray measurements. The bond energies between metal ions including copper ion were discussed by application of the Garrick model with a slight modification.