Revisiting the Polyoxometalate-Based Late-Transition-Metal-Oxo Complexes: The “Oxo Wall” Stands

Terminal oxo complexes of the late transition metals Pt, Pd, and Au have been reported by us in Science and Journal of the American Chemical Society. Despite thoroughness in characterizing these complexes (multiple independent structural methods and up to 17 analytical methods in one case), we have continued to study these structures. Initial work on these systems was motivated by structural data from X-ray crystallography and neutron diffraction and 17O and 31P NMR signatures which all indicated differences from all previously published compounds. With significant new data, we now revisit these studies. New X-ray crystal structures of previously reported complexes K14[P2W19O69(OH2)] and “K10Na3[PdIV(O)­(OH)­WO­(OH2)­(PW9O34)2]” and a closer examination of these structures are provided. Also presented are the 17O NMR spectrum of an 17O-enriched sample of [PW11O39]7– and a careful combined 31P NMR-titration study of the previously reported “K7H2[Au­(O)­(OH2)­P2W20O70(OH2)2].” These and considerable other data collectively indicate that previously assigned terminal Pt-oxo and Au-oxo complexes are in fact cocrystals of the all-tungsten structural analogues with noble metal cations, while the Pd-oxo complex is a disordered Pd­(II)-substituted polyoxometalate. The neutron diffraction data have been re-analyzed, and new refinements are fully consistent with the all-tungsten formulations of the Pt-oxo and Au-oxo polyoxometalate species.