Cu(II) and Cu(I) complexes with 1,2-dithiosquarate as a ligand; from molecular compounds to supramolecular network structures

Four new complexes of copper(II) and/or copper(I) with 1,2-dtsq as a ligand have been synthesized and characterized by single crystal X-ray diffraction methods, [CuII(terpy)(1,2-dtsq)] (1), [CuII(dmen)(1,2-dtsq)]n (2), {[CuII(dmen)2][CuI(1,2-dtsq)]2}n·2nH2O(3) and {[CuII(men)2][CuI (1,2-dtsq)]2}n·nH2O (4) (1,2-dtsq = 1,2-dithiosquarate, dianion of 3,4-dimercapto-1-cyclobutene-1,2-dione; dmen = N,N-dimethylethylenediamine; men = N-methylethylenediamine, terpy = 2,2′:6,2″-terpyridine). Compound 1 consists of neutral [CuII(terpy)(1,2-dtsq)] mononuclear units which are held together by O⋯H–C and van der Waals interactions. Compound 2 is built of neutral [CuII(dmen)(1,2-dtsq)] entities which are connected through weak Cu–S (pairs) and Cu–O (single) interactions into a layer structure. The structures of 3 and 4 feature polynuclear [CuI(1,2-dtsq)]nn- chains, in which dtsq groups are linking copper(I) ions in the μ-1,1, μ-1,1,1 and μ-1,2 bridging modes. The dtsq groups in these chains connect to the copper(II) ions of the [CuIIL2]2+ cations [L being the bidentate dmen (3) and men (4) ligands], but in different manners in the two structures. The connections in compound 3 are unsymmetrical, so that columns of {[CuII(dmen)2][CuI(1,2-dtsq)]2}n where the copper(II) ions bind to 1,2-dtsq oxygen atoms with relatively strong axial bonds may be identified. These columns are further connected to each other through weak axial CuII⋯S interactions, creating a three-dimensional (3D) network with channels containing the solvent water. In compound 4, on the other hand, the two crystallographically independent cations each forms a symmetrical link between the anionic chains through, respectively, O–CuII–O and S–CuII–S axial bonds, again creating a 3D structure with channels running parallel to the chain axis. The reduction of copper(II) to copper(I) by 1,2-dtsq is precluded when the coordination sphere of the copper(II) ion is partially blocked with the tridentate terpy ligand whereas this process occurs when the blocking ligands are the bidentate dmen and men groups.