Electrocrystallization, X-ray structure and electronic properties of the dmit-based salt [MePh₃P] [Ni(dmit)₂]₃

Electrooxidation of [Ni(dmit)₂]^-(dmit = C₃S₅^2- = 4,5-dithiolate-2-thione-1,3-dithiole) in 3:1 acetonitrile-acetone at a Pt wire anode in the presence of methyltriphenylphosphonium bromide electrolyte yields the radical anion salt complex [MePh₃P][Ni(dmit)₂]₃. Black shiny platelet crystals were harvested. They belong to the monoclinic space group P2₁/c, M = 1631.41, a = 21.0872(1), b = 17.4930(2), c = 15.7203(2) Å, β = 107.072(1)°, V = 5543.4(1) ų and Z=4. The crystal packing structure consists of columns of Ni(dmit)₂ units of width one unit separated by columns of MePh₃P⁺ counter-ions. The Ni(dmit)₂ columns are composed of dimers of Ni(dmit)₂ units with non-bonding interactions with six other pairs of Ni(dmit)₂ units. The arrangement of the dimers with respect to each other in the columns has been seen in other phosphonium-based Ni(dmit)₂ complexes and is similar to the packing of κ-BEDT-TTF radical cation salts which have shown superconductivity. Single-crystal temperature-dependent conductivity measurements have shown that this material is semiconducting with a room-temperature conductivity of 0.1 S cm^-1 and a thermal activation energy of 0.22 eV.