SYNTHESIS AND CHARACTERIZATION OF ORGANOMETALLIC CHARGE-TRANSFER SALTS CONTAINING THE BIS(BENZENE)MOLYBDENUM RADICAL CATION

The salt [Mo(eta-C6H6)2][PF6] has been prepared by iodine oxidation of [Mo(eta-C6H6)2] followed by metathesis with NaPF6. The cyclic voltammogram of [Mo(eta-C6H6)2][PF6] in MeCN exhibits a reversible redox couple (E1/2) at -730 mV vs. a saturated calomel electrode (SCE). The solid-state room-temperature EPR spectrum exhibits an isotropic resonance centred at g = 1.993 which is consistent with an assignment of a 2A1g ground state for the 17-electron [Mo(eta-C6H6)2]+ radical cation. The salt [Mo(eta-C6H6)2][FeBr4] has been synthesised from [NEt4][FeBr4] and [Mo(eta-C6H6)2][PF6]. It crystallises in the orthorhombic space group Pbca, a = 18.527(17), b = 12.521(5), c = 14.915(6) angstrom; R and R' = 0.051 and 0.059. The salt [Mo(eta-C6H6)2][FeBr4] consists of segregated chains of cations and anions. The solid-state room-temperature EPR spectrum exhibits two resonances centred at g = 1.987 and 2.008 assignable to the cation and anion respectively. The solid-state magnetic susceptibility data for [Mo(eta-C6H6)2][FeBr4] can be fitted to the Curie-Weiss law between 40 and 300 K with C = 3.93 and theta = -5.4 K. Below 15 K the [FeBr4]- anion sub-lattice orders antiferromagnetically leaving a magnetic susceptibility which is dominated by the [Mo(eta-C6H6)2]+ cations.