Charge-transfer salts with three different stoichiometries for the bimetallic molybdenum complex CpMo(SMe)4MoCp with TCNQ and TCNQF4: structural and magnetic properties

Abstract

The bimetallic complex CpMo(SMe)₄MoCp, 1, oxidizes reversibly at 0.20 and 0.64 V vs. SCE. Reaction with TCNQ and TCNQF₄ leads to three crystalline phases of different stoichiometry, 1:2 in 1·(TCNQ)₂ , 2:1 in 1₂ ·TCNQ and 1:1 in 1·TCNQF₄ , whose crystal structures have been determined by single-crystal X-ray diffraction. Tetramerized TCNQ chains are present in 1·(TCNQ)₂ , separated from each other by 1^AHâ– +radical cations. This 2:1 salt exhibits semiconducting behavior (σ_RT=0.018 S cm^–1). A transition is observed at 160 K in the spin susceptibility and in the EPR linewidth temperature dependence. Below this temperature only the Curie susceptibility of the non-interacting 1^AHâ– +cations remains. In the 2:11₂ ·TCNQ salt, both neutral 1 and oxidized 1^AHâ– +coexist in the solid state, giving rise to alternating … (1^AHâ– +)(TCNQ^AHâ– –)(1^AHâ– +)(TCNQ^AHâ– –) … chains while the empty spaces between the columns are filled with neutral donor molecules. Noticeable differences in the bond distances and angles between neutral1 and oxidized 1^AHâ– +are identified and rationalized. No intermolecular interactions can be found in this compound, whose magnetism is best described by a Curie law for two independentS=1/2 spins. In the 1:1 TCNQF₄ salt, uniform TCNQF₄ stacks are isolated from each other by a honeycomb net of 1^AHâ– +cations. Owing to the large interplanar TCNQF₄–TCNQF₄ distance [3.43(4) Å], the material behaves as a Mott insulator.