One-dimensional coordination polymers constructed from copper(II) ions and chromato bridges: Synthesis, crystal structures and thermal analysis

Abstract

Three 1D coordination polymers, 1∞[Cu(NH3)4CrO4] (1) and 1∞[CuL(H2O)(CrO4)](H2O)(C2H5OH)0.5 with L = bipy (2) and phen (3), have been assembled using chromate(VI) ions as spacers (μ-ĸO:ĸO’ bridging mode). Their crystal structures have been solved. The copper ions in compound 1, whose structure consists of linear chains, show an elongated octahedral geometry, with four ammonia molecules, forming the equatorial plane, and two oxygen atoms arising from two chromato bridges into the apical positions. The ammonia ligands are involved in intramolecular hydrogen bonds with two chromate oxygen atoms, and intermolecular hydrogen bonds with two chromato oxygen atoms from another chain. The crystal structures of compounds 2 and 3 consist of helicoidal chains and solvent molecules. The copper(II) ions in 2 and 3 are five-coordinated (square-pyramidal geometry), with the apical positions occupied by the oxygen atoms from the chromato bridges. Helicoidal chains with opposite chirality are interconnected by π-π stacking interactions established between the organic ligands, resulting in supramolecular layers. The X-band and Q-band EPR spectra of compounds 1–3 are discussed. The total thermal decomposition of these complexes leads to a mixture of CuCr2O4 and CuO, for 1, and of CuCrO2, CuO and Cr2O3, for 2 and 3.