Quasi-one-dimensional bis(ethylenedithio)tetrathiafulvalene charge-transfer salts with paramagnetic group 6 anions

Two new charge-transfer salts of BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene] with paramagnetic anionic. complexes of Group 6 elements have been prepared. The crystal structure of the salt [BEDT-TTF][MoOCl4(H2O)] is unusual in containing no segregated layers of cations and anions but chains of hydrogen-bonded [MoOCl4(H2O)](-) sandwiched between ribbons of BEDT-TTF+ edge linked by S ... S contacts. The structure of [BEDT-TTF](2)[Cr(NCS)(4)(NH3)(2)] consists of alternating layers of [(BEDT-TTF)(2)](+) and [Cr(NCS)(4)(NH3)(2)](-). The molecular packing in the cation layer is unique in comprising double stacks which alternate in orientation with close S ... S contacts not only between cations but between cations and NCS. Both compounds are semiconductors and their magnetic behaviour is dominated by the anions, though there is evidence that the cation ribbons in the molybdenum salt behave as antiferromagnetic chains (J approximate to 110 K).