Elaboration and characterization of a new phosphate Mg1.74Cu1.26(PO4)2·H2O with morphotropic structure

Abstract

The single crystal of Mg1.74Cu1.26(PO4)2·H2O was synthesized hydrothermally and its crystal structure was characterized through X-ray diffraction data. This new phosphate crystallizes in monoclinic system with P21/n space group. Its structure is discussed as a new member of the morphotropic series: MII3(PO4)2·nH2O Three types of cationic sites and two (PO4)3− anions make up its crystal structure. The first and second cationic sites are filled by Cu2+ and Mg2+ respectively, while the last one is occupied by a mixture of the two cations Mg2+ and Cu2+.The connecting of the basic building results in a net framework with two kinds of layers extending parallel to (−101). The first is built up of [Cu2O8] dimers joined by edge-sharing to PO4 tetrahedra. Common edges connecting [(Cu/Mg)2O8(H2O)2] dimers and [MgO6] octahedra form the second layer, which is more corrugated. Adjacent layers are linked by PO4 groups, revealing channels running parallel to the [101] direction and contain H atoms from coordinated H2O. Across these channels, water molecules connect with framework oxygen atoms through OH---O hydrogen bonding interactions.