[Cu-4(H2O)(4)(dmapox)(2)(btc)](n) center dot 10nH(2)O: The first two-dimensional polymeric copper(II) complex with bridging mu-trans-oxamidate and mu(4)-1,2,4,5-benzentetracarboxylato ligands: Synthesis, crystal structure and DNA binding studies

A two-dimensional copper(II) polymer with formula of [Cu-4(H2O)(4)(dmapox)(2)(btc)](n) center dot 10nH(2)O, where dmapox is the dianion of N,N'-bis[3-(dimethylamino)propyl] oxamide and btc is the tetra-anion of 1,2,4,5-benzenetetracarboxylic acid, was synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structure of the complex has been determined by X-ray single-crystal diffraction. The structure consists of crystallized water molecules and neutral two-dimensional copper(II) coordination polymeric networks constructed both by the bis-tridentate mu-trans-dmapox and tetra-monodentate mu(4)-btc bridging ligands. Each btc ligand links four trans-dmapox-bridged binuclear copper(II) building blocks [Cu-2(H2O)(2)(trans-dmapox)](2+) and each binuclear copper(II) building block attaches to two btc ligands forming an infinite 2D layer which consists of 4+4 grids with dimensions of 13.563(5) x 15.616(5) angstrom. The environment around the copper(II) atom can be described as a distorted square-pyramid and the Cu center dot center dot center dot Cu separations through mu-trans-dmapox and mu(4)-btc bridging ligands are 5.225 angstrom (Cu1-Cu1(i)), 5.270 angstrom (Cu-2-Cu-2(ii)), 6.115 angstrom (Cu1-Cu2), 9.047 angstrom (Cu1-Cu2(iii)) and 10.968 angstrom (Cu1-Cu1(iii)), respectively. Abundant hydrogen bonds among the crystallized, the coordinated water molecules, and the uncoordinated carboxyl oxygen atoms cross-link the two-dimensional layers into an overall three-dimensional channel-like framework. The interaction of the copper(II) polymer with calf thymus DNA (CT-DNA) has been investigated by using absorption, emission spectral and electrochemical techniques. The results indicate that the copper(II) polymer interacts with DNA strongly (K-b = 4.8 x 10(5) M (1) and K-sv = 1.1 x 10(4)) and the interaction mode between the copper(II) polymer and DNA may be the groove binding. To the best of our knowledge, this is the first report about the crystal structure and DNA-binding studies of a two-dimensional copper(II) polymer bridged both by the trans-oxamidate and btc ligands. (c) 2008 Elsevier B.V. All rights reserved.