Ab initio study of the electronic spectrum of the heptacyanovanadate(III) complex

Extensive ab initio CASSCF/CASPT2 computations have been performed to calculate all ligand field and the lowest charge transfer transitions of the [V(CN)7]4− anion. The electronic structure is analysed in terms of D5h and C2v point group symmetries, i.e., an idealised pentagonal bipyramidal structure and an axially bent structure, respectively. The CASPT2 calculated values for the ligand field transitions reproduce to a fair extent the peak values of the experimental spectra. No significant differences in bonding characteristics between equatorial and axial ligands are found. Spin–orbital coupling induces noticeable splitting of the excited triplet states but only very small singlet–triplet mixings. The lowest calculated charge transfer state is of the ligand-to-metal type and situated at around 40 000 cm−1 above the ground state. The lowest metal-to-ligand states have been found at least 6000 cm−1 higher in energy.