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(OH2)6]3+ 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(OH2)6]3+ 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(OH2)6]3+
cation. However, the ligand-field analysis is inconsistent with the profiles of electronic transitions between ligand-field terms.