A Novel Copper(II)–Hydrogen Oxalate Coordination Polymer Showing a New Coordination Mode

Abstract

A novel Cu(II) coordination polymer of general empirical formula {[Cu(μ-HC2O4)2(H2O)2][Cu(HC2O4)2]∙6H2O}n (1) has been synthesized and characterized by single-crystal X-ray diffraction technique. The complex (1) crystallizes in the triclinic form with P-1 space group. It is quite surprising that single crystal X-ray analysis of 1 illustrates the presence of hydrogen oxalate ligand in the coordination environment of Cu(II) ion. Because oxalate is not present in the starting reaction mixture, it may be derived from the reduction of squarate ligand. In 1, Cu(II) ions exhibit two different coordination environments, forming a distorted octahedral geometry. The Cu1 is coordinated with six oxygen atoms from two bidentate HC2O4− and two aqua ligands, while Cu2 is coordinated with six oxygen atoms from four HC2O4− ligands. The HC2O4− ligand acts in two different coordination modes, as a bidentate and an unprecedented tridentate bridging coordination mode.