Structure and stability of carboxylate complexes. Part VIII. Crystal and molecular structures of copper(II) hydrogen maleate tetrahydrate and copper(II) maleate hydrate

Abstract

The crystal and molecular structures of copper(II) hydrogen maleate tetrahydrate and copper(II) maleate hydrate have been determined by three-dimensional X-ray methods. In copper(II) hydrogen maleate (monoclinic, a= 3·594, b= 18·79, c= 9·69 Å, γ= 93·25°, space group l2/m, diffractometer data, R= 0·039) the copper atoms are co-ordinated only by water molecules to form [Cu(H₂O)₄]_n²ⁿ⁺ chain cations which are hydrogen bonded to the planar hydrogen maleate anions. In the hydrogen maleate anion the intra-molecular hydrogen bond is 2·409 Å. The copper co-ordination octahedron is distorted, Cu–OH₂(bridging) 1·959 and 2·682 Å, and Cu–OH₂(non-bridging) 1·933 Å. In copper maleate tetrahydrate (monoclinic, twinned, a= 8·78, b= 7·88, c= 5·35, γ= 125·1°, P2₁, photographic data, R= 0·096) the copper atom is in a five-co-ordinate square-pyramidal environment. The ligands are a water molecule, Cu–OH₂, 2·26 Å, a chelating maleate group forming a seven-membered chelate ring, and two oxygen atoms of two other maleate groups. In the basal plane the average copper–oxygen bond length is 1·99 Å. Each maleate group is bound to three copper atoms to form a polymeric sheet. The sheets are joined by hydrogen bonding.