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.