Synthesis of a hierarchy of zinc oxalate structures from amine oxalates

A hierarchy of novel zinc oxalates including monomers and dimers has been prepared by reaction of amine oxalates with zinc ions, the amine oxalates having been characterized for the first time. In most of the amine oxalates one of the carboxyl groups transfers a proton to the amino nitrogen, leaving the other carboxyl group free to form hydrogen bonds. The zinc oxalates obtained are composed of a network of ZnO6 octahedra and oxalate units, and possess zero-, one-, two- and three-dimensional structures. The monomer, dimer, and chain zinc oxalates are the first members of the hierarchy of structures. Relationships amongst these various oxalate structures are noteworthy and give indications as to the manner in which these structures are formed. Thus, the three-dimensional structure can be formed by the linking of layers, and the layer structure by condensation of linear chains. The isolation and characterization of a hierarchy of zinc oxalates of differing dimensionalities assumes significance in the light of the recent finding that low-dimensional structures transform to higher, more complex structures in the phosphate family.