Syntheses, crystal structures and conducting properties of new homoleptic copper (II) dithiocarbamate complexes

Five new homoleptic dithiocarbamate complexes of the general formula [Cu(L)2] [L = L1 (N-benzyl-N-furfuryl dithiocarbamate) (1); L2 (N,N-difurfuryldithiocarbamate) (2); L3 (4-ethoxycarbonylpiperidine-1-dithiocarbamate) (3); L4 (4-ethoxycarbonylpiperazine-1-dithiocarbamate) (4) and L5 (N-benzyl-N-3-methylpyridyl dithiocarbamate) (5) have been prepared and characterized by elemental analysis, spectroscopy (IR, UV–Vis, EPR), magnetic moment determination and cyclic voltammetry; their structures have been elucidated by X-ray crystallography. Variations in sterically demanding substituents on the dithiocarbamate units lead to different structures. 1, 2, 3 and 4 are Cu(dtc)2 moieties in which the copper atoms occupy square planar environments which are connected via weak interactions in axial positions to form centrosymmetric dimers. The weak Cu⋯S distances vary significantly in the four complexes. By contrast 5 is a monomer with two molecules in the asymmetric unit. The supramolecular architecture in the five complexes has been sustained in the solid state by, C–H⋯S, C–H⋯O, π⋯π and C–H⋯π (chelate, CuS2C) interactions. The electrical properties of all the complexes studied by the impedance spectroscopic technique in the 303–373 K temperature range show semiconducting properties with σrt = 10−7–10−5 S cm−1 and Ea = 0.23–0.66 eV. The dielectric properties of the complexes have been measured at variable frequency (100 Hz–5 MHz) in the 303–373 K range; and show notably that complex 3 has a high dielectric constant.