Electronic structures and d—d spectra of vanadium( IV ) and VO ²⁺ complexes: discrete variational Xα calculations

Discrete Variational Xα(DVXα) calculations at three successive levels of approximation have been carried out for the vanadium(IV) complexes VCl4, [VCl5]–, [VOCl4]2–, [VO(NCS)4]2–, [VO(NCS)4(OH2)]2–, [VO(CN)5]3–, [VO{OC(NH2)2}2Cl2] and [VO(NMe3)2Cl2]. The electronic structures and the nature of the metal-ligand bonding are described and compared with previous theoretical results and a detailed comparison between observed and computed d–d electronic transition energies is presented. Near-quantitative agreement is obtained for the observed band maxima. The calculated assignments from the most accurate calculations are also in agreement with experiment. In contrast to previous theoretical treatments of [VOCl4]2–, which predict the reversed order of the first two absorptions, the DVXα results yield the correct energy-level scheme. The ESR g and A values for this species are also well reproduced theoretically.