Structure and bonding of the vanadium(III) hexa-aqua cation. 1. Experimental characterization and ligand-field analysis.

Spectroscopic and crystallographic data are presented for salts containing the V(OH(2))(6) cation, providing a rigorous test of the ability of the angular overlap model (AOM) to inter-relate the electronic and molecular structure of integer-spin complexes. High-field multifrequency EPR provides a very precise definition of the ground-state spin-Hamiltonian parameters, while single-crystal absorption measurements enable the energies of excited ligand-field states to be identified. The EPR study of vanadium(III) as an impurity in guanidinium gallium sulfate is particularly instructive, with fine-structure observed attributable to crystallographically distinct V(OH(2))(6) cations, hyperfine coupling, and ferroelectric domains. The electronic structure of the complex depends strongly on the mode of coordination of the water molecules to the vanadium(III) cation, as revealed by single-crystal neutron and X-ray diffraction measurements, and is also sensitive to the isotopic abundance. It is shown that the AOM gives a very good account of the change in the electronic structure, as a function of geometric coordinates of the V(OH(2))(6) cation. However, the ligand-field analysis is inconsistent with the profiles of electronic transitions between ligand-field terms.