Single-crystal electron paramagnetic resonance investigation of γ-irradiated K2[MoO(O2)F4]·H2O and molybdenum-doped K2[Nb(O2)F5]·H2O
Abstract
The single-crystal EPR spectra of γ-irradiated pure K2[MoO(O2)F4]·H2O and molybdenum-doped K2[Nb(O2)F5]·H2O, each giving rise to a set of resonances both at low and high fields relative to that of the free-electron g value, have been investigated. The high-field lines are similar for both complexes and are attributed to an electron-excess species [MoOF4]–, formed from [MoO(O2)F4]2– by radiation damage followed by rearrangement due to the extra electron. The EPR parameters for this radical are g∥= 1.932(1), g⊥= 1.896(1), A∥(19F)= 0.80(5) and A⊥(19F)= 4.65(5) mT. The low-field lines of the Mo-doped niobium compound are due to a niobium hole species, [Nb(O2)F5]–, having the unpaired electron occupying the non-bonding orbital of the peroxo oxygen atoms. However, the low-field lines of the pure molybdenum complex are due to a hole species, [Mo(O2)F4]+, having spin-Hamiltonian parameters gxx= 2.037(1), gyy= 1.999(1), gzz= 2.011(1), Axx(19F)= 1.81(5), Ayy(19F)= 0.70(5) and Azz(19F)= 2.81(5) mT. Further support for the assumed species comes from extended Hückel molecular orbital calculations. The crystal structure of the pure molybdenum complex was redetermined.