Synthesis and crystal structure of a novel charge transfer salt, (TMT-TTF)4[HPMo12O40]

A new charge transfer salt based on TMT-TTF (tetramethylthiatetrahiafulvalene) and Keggin-type anion [PMo12O40]3- was electrochemically synthesized and its structure was determined by X-ray diffraction analysis. Monoclinic, P21/n, a=12.766 (2) Å, b=15.096 (3) Å, c=24.323 (5) Å, β=98.28(3)°, V=4638.9 Å3, Z=2, R1=0.0777 (I>2σ). The crystal structure of (TMT-TTF)4[HPMo12O40] presents a 3D packing through the S⋯S contacts between donors and the interactions between organic and inorganic layers. The layers of the organic donor and inorganic acceptor are alternatively arranged in (011) and (101) planes. The organic layer is formed by two crystallographically independent TMT-TTF molecules (A and B) which form two kinds of TMT-TTF dimers. The charges of A and B molecules are respectively deduced to +0.5 and +1 on the basis of the intramolecular bond lengths. The anions adopt simple monoclinic packing arrangements and each anion is surrounded by eight TMT-TTF molecules. ESR spectrum at 110 K displays distinct TMT-TTF+ and Mo5+ signals, the anion [PMo12O40]3- is reduced by one electron. The compound shows semi-conductor behavior at room temperature with σ≈10−3 S cm−1.