Spacer-Dependent Structural and Physicochemical Diversity in Copper(II) Complexes with Salicyloyl Hydrazones: A Monomer and Soluble Polymers

Complexation of copper(II) with a series of heterodonor chelating Schiff bases (LL) of salicylic acid hydrazide and aliphatic or cycloaliphatic ketones affords soluble one-dimensional (1D) metallopolymers containing Schiff bases as bridging ligands. Single-crystal X-ray diffraction results reveal nanometer-sized metallopolymeric wires [Cu(μ-LL)2]n with off-axis linkers and a zigzag geometry. Octahedrally coordinated copper centers, exhibiting a Jahn−Teller distortion, are doubly bridged by two Schiff-base molecules in the μ2−η1,η2 coordination mode. The use of dibutylketone with long alkyl chains as a component for Schiff base formation leads to a distorted square planar monomeric copper(II) complex [Cu(LL)2], as evidenced by its X-ray crystal structure. The compounds are characterized by elemental analyses and IR and UV−vis spectroscopy, as well as magnetic susceptibility and cyclic voltammetry measurements. Electrochemical studies on the complexes reveal an existence of polymeric and monomeric forms in solution and the dependence of Cu(II)/Cu(I) reduction potentials on alkyl groups of salicyloyl hydrazone ligands. Polymeric complexes form conducting films on Pt electrodes upon multicycle potential sweeps.