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

Abstract

Electro-oxidation of a solution of [Bu4N][Ni(dmit)2] (dmit = C3S52− = 1,3-dithiole-2-thione-4,5-dithiolate) in the presence of a large excess of 1,1,2,2-tetramethylguanidinium chloride (Me4GuaCl) or hexamethylguanidinium iodide (Me6GuaI) yields black crystals of [Me4Gua][Ni(dmit)2]2 (1) and [Me6Gua][Ni(dmit)2]2 (2), respectively. The X-ray structures of 1 and 2 were determined in space group P1 (No. 2) with for 1 a = 5.924(3), b = 8.078(3), c = 18.088(6) Å, α = 89.71(3), β = 83.74(3), γ = 76.12(3)°, V = 835.1(6) Å3, Z = 1, R1 = 0.031, wR2 = 0.077, and for 2 a = 6.0080(4), b = 8.2739(5), c = 18.1173(9) Å, α = 91.235(5), β = 93.978(5), γ = 102.278(6)°, V = 877.28(9) Å3, Z = 1, R1 = 0.027, wR2 = 0.069. The anionic 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 intermolecular orbital overlap integral calculations point towards a weak two-dimensional 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 cm−1 for 2. Both compounds behave as semiconductors in the temperature range 300-100 K with Ea = 0.15 and 0.10 eV for 1 and 2, respectively. Montgomery single-crystal measurements on compound 2 showed that the anisotropy in the bc plane is small.