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 g_xx= 2.037(1), g_yy= 1.999(1), g_zz= 2.011(1), A_xx(¹⁹F)= 1.81(5), A_yy(¹⁹F)= 0.70(5) and A_zz(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.