ESR Study of radicals formed in γ-irradiated single crystals of K2NbOF5 · H2O

A single-crystal ESR study has been made of K2NbOF5· H2O γ irradiated at 77°K. Two 93Nb-centered radicals were observed at 77°K; one of these is shown to be [NbOF5]3− with a d1 configuration and a dxy ground state and the g, A (93Nb), and A (19F) tensors for this radical have been evaluated. The A (19F) fluorine superhyperfine interaction tensor for the equatorial fluorine ligands indicates strong in-plane π bonding between the niobium 4dxy orbital and the 2py orbitals of fluorine. The g and A (93Nb) parameters have also been used to calculate molecular orbital coefficients for this complex. On warming, the [NbOF5]3− radical decays at −80°C leaving a second radical, the ESR spectra of which suggest that it is a hole species formed by the removal of an electron from [NbOF5]2−.