Metal-phenoxyalkanoic acid interactions. : Part 19. The divalent metal complexes of 2-carboxyphenoxyacetic acid and the crystal structures of catena-μ-[ (2-carboxylato-O)phenoxyacetatoaquacopper(II)] and diaquabis(2-carboxyphenoxyacetato)copper(II)

Abstract

The crystal structures of two chemical polymorphs of copper(II) 2-carboxyphenoxyacetate (OCPAH 2) have been determined by X-ray diffraction. The first complex with formula [Cu(OCPA)(H 2O)] n ( 1) is a step polymer with inversion related square pyramidal copper centres comprising an axial water molecule [Cu—Ow, 2.192(8) Å], two oxygens from a bidentate chelate phenoxy group [Cu—O(carboxyl), 1.921(9) Å; CuO(ether), 2.050(7) Å], an oxygen from the 2- carboxyl group [Cu—O, 1.906(8) Å] and one from a bridging carboxylate group [Cu—O, 1.941(8) Å]. Polymorph ( 2) [Cu(OCPAH) 2(H 2O) 2], is square planar with two waters [Cu—Ow, 1.912(10) Å], and trans-related phenoxy ligands [Cu—O, 1.912(10) Å] bonded to the metal through the phenoxy carboxyl group. The 2-carboxyl group is protonated and forms cyclic hydrogen bonds with adjacent complex units [OO, 2.92 Å] to give a stable polymer network. Data also confirms isomorphism in the divalent OCPA complexes of Co, Ni and Mg, having the formula [M(OCPA)(H 2O) 3].