Synthesis and Chemistry of Trichalcogenophosphonates

Metal organophosphonates have been extensively studied over the last thirty years due to their potential and practical applications as ion exchangers, sorbents, sensors, proton conductors, nonlinear optical materials, catalysts and hosts for the intercalation of a broad spectrum of guests. They have also been widely used as key building blocks in the self-assembly of molecular clusters and supramolecular networks. In stark contrast the heavier chalcogen (sulphur, selenium, tellurium) containing homologs of these oxygen containing metal organophosphonates have attracted far less attention, predominately due to a lack of a reliable synthetic route to these systems. However, we have recently reported upon a clean and high yielding route to such trichalcogenophosphonates containing three sulphur or three selenium atoms in place of the three oxygen atoms in metal organophosphonates. We now propose to exploit our recent advances in this area by carrying out a full study on the reactivity and coordination chemistry of these new compounds as well as extending our synthetic route to prepare novel compounds containing two or more trichalcogenophosphonate groups.These new compounds and materials will be studied for a variety of applications including as new porous materials for the removal of heavy metal contaminants such as mercury and arsenic from contaminated water supplies. Organophosphonate based materials are already used in water treatment for the removal of limescale whereby the hard calcium metal ion binds strongly to the hard oxygen atoms in the organophosphonate group. Replacement of one or more of the oxygens with the larger, softer sulphur atom in our new compounds will result in a new material capable of binding strongly to larger, softer metal ions such as mercury cations, hence removing them from the water supply.In addition we will study the use of these trichalcogenophosphonate compounds as reagents for the synthesis of organic and bio-organic compounds, for example in the conversion of ketones (R2C=O) to thioketals (R2C=S). It is expected that their much increased solubility in polar solvents over existing reagents for this reaction will allow the use of less harsh and more green-chemistry conditions (lower temperatures and less solvent).