Squarato-metal(II) complexes: Part 5. Polynuclear copper(II) complexes bridged by squarate and croconate dianions

Two polynuclear Cu(II) complexes namely 1-D polymeric {[Cu(DPA)(μ1,2-C4O4)(H2O)]∙2H2O}n (1) and the tetranuclear {[Cu2(DPA)2(μ-1,1,2,3-C5O5)(H2O)](ClO4)2∙ H2O}2 (2) where DPA = bis(2-pyridylmethyl)amine, C4O42− = squarate dianion, and C5O52− = croconate dianion were synthesized and structurally characterized by X-ray crystallography. The C4O42− and C5O52− dianions are bridging the Cu2+ centers via a μ-1,2-bis(monodentate) and μ-1,2,3-bis(bidentate)-μ-1-(monodentate) bonding modes in complexes 1 and 2, respectively. A new coordination bonding mode is reported for the bridged croconate in the later complex. Hydrogen bonds stabilize the supramolecular 2D and 3D systems in the complexes. Magnetic susceptibility measurements for the 1D-polymeric complex 1 reveal insignificant coupling between the Cu(II) ions, whereas the tetranuclear croconato complex 2 exhibits moderate antiferromagnetic coupling between the central Cu(II) ions (J = − 9.4 cm–1) and weak antiferromagnetic coupling between the terminal Cu(II) ions (J = − 5.1 cm–1).