Chemists force platinum partnership

Chemical bonds between metals and oxygen to form metal-oxo species are common for metals on the left of the periodic table, as electrons from oxygen atoms transfer to vacant d-orbitals in the metal atoms. But metal-oxo species become increasingly less stable for metals on the right hand side of the table, because the d-orbitals of these metals already contain electrons, which repulse the oxygen atoms.

All previous attempts to synthesise metal-oxo species with elements such as gold, platinum, silver, iridium and rhodium had been unsuccessful. However, such metal-oxo species were thought to form briefly as intermediates in numerous catalytic reactions, including those that take place in catalytic converters and fuel cells.

To create their platinum-oxo compound, the chemists from Emory University, Atlanta, and the University of New Mexico, Albuquerque, reacted the platinum salt K₂PtCl₄ with the polytungstate cluster A-?-Na₉PW₉O₃₄ in water. They thought that the presence of polytungstate molecules might help to prevent the oxygen atoms from being pushed away. Eventually this reaction produced thermally stable brown crystals that elemental analysis showed to have the chemical formula K₇Na₉[Pt(O)(H₂O)(PW₉O₃₄)₂].21.5H₂O, in which a platinum(iv)-oxo compound is flanked by two polytungstate ligands. X-ray diffraction studies confirmed the presence of a platinum-oxo bond.

’Since this metal-oxo is a unique compound, both its physical properties and its chemical reactivities should provide new insights and break new ground,’ predicts lead researcher Craig Hill of Emory University. Hill and his team envisage the platinum-oxo compound will act as a model for the metal-oxo intermediates that form in catalytic converters and fuel cells, leading to improvements in these technologies. Meanwhile, Hill now plans to create metal-oxo bonds with other late transition metals.

Jon Evans