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

Abstract

Electrooxidation of [Ni(dmit) ₂ ] ^- (dmit=C ₃ S ₅ ^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 [MePh ₃ P][Ni(dmit) ₂ ] ₃ . Black shiny platelet crystals were harvested. They belong to the monoclinic space group P2 ₁ /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) Å ³ and Z=4. The crystal packing structure consists of columns of Ni(dmit) ₂ units of width one unit separated by columns of MePh ₃ P ⁺ 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.