SYNTHESIS AND CRYSTAL-STRUCTURE OF [1,1,2,2-TETRAMETHYLGUANIDINIUM][NI(DMIT)(2)](2) AND [HEXAMETHYLGUANIDINIUM] [NI(DMIT)(2)](2) (DMIT=1,3-DITHIOLE-2-THIONE-4,5-DITHIOLATE) - INTERMOLECULAR ORBITAL OVERLAP INTEGRAL CALCULATIONS AND ELECTRICAL CONDUCTIVITIES

Electro-oxidation of a solution of [Bu(4)N][Ni(dmit)(2)] (dmit=C3S52-= 1,3-dithiole-2-thione-4,5-dithiolate) in the presence of a large exces s of 1,1,2,2-tetramethylguanidinium chloride (Me(4)GuaCl) or hexamethy lguanidinium iodide (Me(6)GuaI) yields black crystals of [Me(4)Gua][Ni (dmit)(2)](2) (1) and [Me(6)Gua][Ni(dmit)(2)](2) (2), respectively. Th e X-ray structures of 1 and 2 were determined in space group P (1) ove r bar (No. 2) with for 1 a=5.924(3), b=8.078(3), c=18.088(6) Angstrom, alpha=89.71(3), beta=83.74(3), gamma=76.12(3)degrees, V=835.1(6) Angs trom(3), Z=1, R1=0.031, wR2=0.077, and for 2 a=6.0080(4), b=8.2739(5), c=18.1173(9) Angstrom, a alpha=91.235(5), beta=93.978(5), gamma=102.2 78(6)degrees, V=877.28(9) Angstrom(3), Z=1, R1=0.027, wR2=0.069. The a nionic part of the structures is approximately the same. The slightly dimerized Ni(dmit)(2) units form layers with a two-dimensional network of S...S interactions in the ab plane. For both compounds intermolecu lar orbital overlap integral calculations point towards a weak two-dim ensional conduction pathway in the ab plane. Conductivity measurements indicate a room temperature value of 0.08 S cm(-1) for 1 and 0.03 S c m(-1) for 2. Both compounds behave as semiconductors in the temperatur e range 300-100 K with E(a)=0.15 and 0.10 eV for 1 and 2, respectively . Montgomery single-crystal measurements on compound 2 showed that the anisotropy in the be plane is small.