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

The bimetallic complex CpMo(SMe)(4)MoCp, 1, oxidizes reversibly at 0.20 and 0.64 V vs. SCE. Reaction with TCNQ and TCNQF(4) leads to three crystalline phases of different stoichiometry, 1:2 in 1(TCNQ)(2), 2:1 in 1(2).TCNQ and 1 : 1 in 1.TCNQF(4), 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(.+) radical cations. This 2:1 salt exhibits semiconducting behavior (sigma(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(.+) cations remains. In the 2:11(2).TCNQ salt, both neutral 1 and oxidized 1(.+) coexist in the solid state, giving rise to alternating...(1(.+))(TCNQ(.-))(1(.+))(TCNQ(.-))...chains while the empty spaces between the columns are filled with neutral donor molecules. Noticeable differences in the bond distances and angles between neutral 1 and oxidized 1(.+) are identified and rationalized. No intermolecular interactions can be found in this compound, whose magnetism is best described by a Curie law for two independent S=1/2 spins. In the 1: 1 TCNQF, salt, uniform TCNQF(4) slacks are isolated from each other by a honeycomb net of 1(.+) cations. Owing to the large interplanar TCNQF(4)-TCNQF(4) distance [3.43(4) Angstrom], the material behaves as a Mott insulator.