Preparation, structural, electrical and magnetic properties of tetrathiafulvalene-Au(pdS)(2) salts (pds = pyrazine-2,3-diselenolate)

The combination of the electron donor tetrathiafulvalene, ttf, with the gol d complex bis(pyrazine-2,3-diselenolate)aurate(III), Au(pds)(2)(-), afforde d three different compounds depending on the preparative conditions: (ttf)( 2)[Au(pds)(2)](2) (1), (ttf)(3)[Au(pds)(2)](2) (2) and (ttf)(3)[Au(pds)(2)] (3) (3). Compound 1 was obtained by interdiffusion Of (ttf)(3)(BF4)(2) and (NBu4n)Au(pds)(2) in acetonitrile. Compounds 2 and 3 were obtained by elect rocrystallisation from ttf and (NBu4n)Au(pds)(2) solutions in dichlorometha ne and acetonitrile respectively. These compounds were characterised by X-r ay diffraction and electrical and magnetic studies. In the crystal structur e of compound 1 are two types of ttf motifs dimers and isolated units. In t he structures of compounds 2 and 3 the ttf units are arranged in trimers. I n compound 2 the ttf units form trimerised segregated stacks separated by A u(pds)(2) units with their long axis almost parallel to the stacking axis. In 3 each ttf trimer is surrounded by a cage of four Au(pds)(2) units, and is arranged perpendicularly to the nearest neighbouring trimers. Compounds 1 and 2 exhibit a semiconducting behaviour with room temperature conductivi ties of 10(-4) S cm(-1) and 10(-2) S cm(-1), respectively. Compound 2 is es sentially diamagnetic, while compound 1 shows a large paramagnetic suscepti bility, at room temperature chi (p) = 13 x 10(-4) emu mol(-1), following a Curie-Weiss law above 50 K. Compound 3 is paramagnetic with a temperature i ndependent EPR signal in the range 100-300 K.