Chapter 5. Metal Phosphonates and Arsonates Containing an Auxiliary Ligand

Abstract

Metal phosphonates are a class of important compounds that are able to exhibit a variety of open-framework structures and have many potential applications in catalysis, ion exchange, magnetism, and materials chemistry. When an auxiliary ligand is present, their structures and properties can be changed significantly. An acidic polydentate ligand such as oxalate and benzotricarboxylate usually participates in the framework formation, and these inorganic–organic hybrids are normally layered or 3D. In a few cases, these auxiliary ligands can also be intercalated between two metal phosphonate layers. For the basic auxiliary ligands such as 4,4′-bipy and piperazine, the metal phosphonate moieties (clusters, 1D chains, or 2D layers) are further bridged into aggregations with a higher dimensionality. The use of bidentate or tridentate chelating auxiliary ligand such as 2,2′-bipy and terbipy usually reduces the metal coordination sites available for the phosphonate ligands, hence the resultant compounds are able to display a variety of low dimension structures such as clusters or 1D chains. Recently these synthetic approaches have been successfully applied to the metal arsonates which display many similar features to those of metal phosphonates.