Synthesis and structural studies of mono- and dinuclear Cu(II) complexes with an ONO donor Schiff base ligand: Self-assembly and sulfato-bridged

Five Cu(II) complexes, [CuL(NO3)] (1), [CuLBr][CuLCH3OH]2Br2 (2), [CuLN3] (3), [CuL(ClO4)]2 (4) and [H2OLCu(μ-SO4)CuLH2O] (5), where L is the salicylaldehyde semicarbazone tridentate Schiff base ligand, have been synthesized and characterized by elemental analysis, FT-IR, UV–Vis and mass spectroscopy. The structures of compounds 2, 4 and 5 have been determined by single-crystal X-ray diffraction analyses. The structure of 2 contains both a mononuclear and a dinuclear species as distinct entities. The coordination geometry around the copper(II) ion in the mononuclear species is four coordinated square planar, whereas the dinuclear complex cation is five coordinated square pyramidal in which each copper(II) ion has a distorted square pyramidal geometry. In the mononuclear species, L acts as a tridentate ligand and the fourth position at the Cu ion is occupied by the Br anion, while in the dinuclear species, L acts as a bridging tridentate ligand connecting two Cu(II) ions, so there is an intramolecular copper–copper separation of 3.034 A and the apical position of each Cu ion is occupied by the oxygen of a methanol molecule. Complex 4 is a dinuclear species, in which each copper(II) ion exhibits a distorted square pyramidal geometry, which is similar to complex 2. The L ligand adopts a tridentate bridging mode with a copper–copper distance of 3.011 A. The apical position is occupied by a perchlorate anion. The molecular structure of 5 shows that it is a sulfato bridged dimeric Cu(II) complex with an intramolecular copper–copper separation of 4.733 A. The coordination geometry around each copper is five coordinated square pyramidal with two oxygen and one nitrogen atom from the tridentate ligand, L, and an oxygen from a coordinated water in equatorial positions and an oxygen from the bridging sulfato group in the axial position.