Structure and Bonding of the Vanadium(III) Hexa-Aqua Cation. 1. Experimental Characterization and Ligand-Field Analysis

Abstract

Spectroscopic and crystallographic data are presented for salts containing the [V(OH(2))(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(OH(2))(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(OH(2))(6)](3+) cation. However, the ligand-field analysis is inconsistent with the profiles of electronic transitions between ligand-field terms.

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

“…In this complex, the ammine ligands are pure σ-donors, in contrast to the complicated, anisotropic π-bonding that is found for aqua ligands, which leads to extensive ZFS for nominally octahedral, HS hexaaqua complexes. [32][33][34] In addition, the octahedral d 8 ) and 330 GHz (11 cm -1 ), typical for HFEPR. Only with the last of these is a magnetic dipole allowed transition possible at an accessible magnetic field. )…”

“…2+ has a small ZFS, presumably arising from anisotropy in the aqua ligands, as described for other highspin ions by Tregenna-Piggott. 30,[32][33][34] In these cases, a trigonal splitting results, which for V II as a dopant in corundum (Al 2 2+ as in the oxide lattice.…”

“…24 Another locus of these older theories is the place where they were brought into full flower, Copenhagen, Denmark. The work by Jesper Bendix [25][26][27] and Høgni Weihe 28 and their co-workers in Copenhagen, together with Philip L. W. TregennaPiggott in Switzerland, [29][30][31][32][33][34][35][36][37] represent superb examples of state-of-the-art experimental (not only HFEPR, but also optical and vibrational spectroscopy, and most significantly, inelastic neutron scattering (INS) 31 ) and computational studies. In particular, Bendix has directly compared LFT to the current luminary, DFT.…”

Electronic structure of V3+ in NaMgAl(ox)3·9H2O probed by Fourier transform spectroscopy

“…Pseudooctahedral V 3+ has a 3 T 1g ground state that is difficult to study by classical electron resonance spectroscopy due to the large axial zero-field splitting (ZFS). Study of the ground-state electronic structures of integer-spin systems, like V 3+ , has received renewed attention in part due to the evolution of high field, high-frequency electron paramagnetic resonance (HFEPR) and inelastic neutron scattering spectroscopies [2][3][4][5].…”

Vibrational spectra of hexaaquacomplexes. XII. On the possible anion disorder in selenate alums: prediction of the crystal structure and vibrational spectra of KAl(SeO4)2·12H2O and related alums

“…Later more researchers joined this group and valuable papers were published [31][32][33][34][35][36][37][38][39]. The most important discovery of the Australian group is a precise and straightforward criterion for distinguishing α and β alums, on the basis of some geometrical/structural arguments.…”