Ground-State Electronic Structure of Vanadium(III) Trisoxalate in Hydrated Compounds

The ground-state electronic structures of K3V(ox)3.3H2O, Na3V(ox)3.5H2O, and NaMgAl1-xVx(ox)3.9H2O (0xor= 1, ox = C2O42-) have been studied by Fourier-transform electronic absorption and inelastic neutron scattering spectroscopies. High-resolution absorption spectra of the 3Gamma(t2g2) --1Gamma(t2g2) spin-forbidden electronic origins and inelastic neutron scattering measurements of the pseudo-octahedral [V(ox)3]3- complex anion below 30 K exhibit both axial and rhombic components to the zero-field-splittings (ZFSs). Analysis of the ground-state ZFS using the conventional S = 1 spin Hamiltonian reveals that the axial ZFS component changes sign from positive values for K3V(ox)3.3H2O (D approximately +5.3 cm-1) and Na3V(ox)3.5H2O (D approximately +7.2 cm-1) to negative values for NaMgAl1-xVx(ox)3.9H2O (D approximately -9.8 cm-1 for x = 0.013, and D approximately -12.7 cm-1 for x = 1) with an additional rhombic component, |E|, that varies between approximately 0.8 and approximately 2 cm-1. On the basis of existing crystallographic data, this phenomenon can be identified as due to variations in the axial and rhombic ligand fields resulting from outer-sphere H-bonding between crystalline water molecules and the oxalate ligands. Spectroscopic evidence of a crystallographic phase change is also observed for K3V(ox)3.3Y2O (Y = H or D) with three distinct lattice sites below 30 K, each with a unique ground-state electronic structure.