Derivatized and Nanoscale Polyoxometalate Cluster Anions

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Dr Michael T. Pope, Chemistry Department, Georgetown University, is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program, to investigate the chemistry of polyoxometalate species. This research is directed towards developing robust, water-stable, functionalized organic derivatives of (a) polytungstate anions containing 10-30 tungsten atoms and one to several other atom types that can be used as sites of further derivatization and (b) massive, soluble discrete polyoxoanions of nanoscale dimensions that contain 100+ metal atoms. The ability to derivatize rhodium containing type (a) complexes at the rhodium will be used to couple the polyoxometalate to ribosomes for phasing of x-ray data. Additional type (a) species will be prepared with multiple sites for derivatization. These species can be utilized for supporting agents to attach catalytically active polyoxoanions to polymer substrates, for selective electron-density imaging, and other applications. Type (b) complexes are exemplified by a 76- anion containing 12 As, 16 Ln, 148 W, and 524 O atoms plus 36 water molecules. This anion is water soluble and has been crystallographically characterized. Synthetic strategies will be designed for analogues of this species in which As is substituted by other group 15 atoms and for those that contain a variety of lanthanides. The preparation of even larger clusters will be devised. The hydrolytic stability, structures, electrochemistry and other properties will be investigated in solution for these large anions. Methods will be designed to couple these clusters anions into designed, extended assemblies. The polyoxometalates are a large ions composed of metal and oxygen atoms. They are of interest because they are wholly inorganic, and thus should be quite robust under many conditions. This investigation will explore the chemistry of two classes of these ions. The first contains 10-30 metal atoms and has centers that can be linked to other chemical species. The second class is composed of very massive ions that contain hundreds of atoms and are nano-sized. Both classes are unusual for because they dissolve in and are stable in water. They have potential applications as ion-exchange and host/guest materials, catalysts, conducting and magnetic materials, and display devices.