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

Abstract

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 (17)O and (31)P 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 K(14)[P(2)W(19)O(69)(OH(2))] and "K(10)Na(3)[Pd(IV)(O)(OH)WO(OH(2))(PW(9)O(34))(2)]" and a closer examination of these structures are provided. Also presented are the (17)O NMR spectrum of an (17)O-enriched sample of [PW(11)O(39)](7-) and a careful combined (31)P NMR-titration study of the previously reported "K(7)H(2)[Au(O)(OH(2))P(2)W(20)O(70)(OH(2))(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.

Experimental and Computational Evidence of Highly Active Fe Impurity Sites on the Surface of Oxidized Au for the Electrocatalytic Oxidation of Water in Basic Media

“…For Fe‐free Au 2 O 3 , the *O intermediate is high in energy, and the potential determining step is therefore Reaction (5) (*OH oxidation to *O), while for Fe‐Au 2 O 3 , the *O intermediate is relatively more stable and the potential determining step is Reaction (6) (*O oxidation to *OOH). These changes can be explained as follows: because the d orbitals of Au are nearly filled and are unable to form π bonds with oxygen, Au sites bind oxo species very weakly, whereas Fe has fewer d electrons and can form π bonds with oxygen, leading to more stable Fe=O structures . Consequently, the binding energetics of OER reaction intermediates attached to Fe cations bound to the surface of Au 2 O 3 are more optimal than those of intermediates attached to Au cations.…”

Synthesis and reactivity of a mononuclear non-haem cobalt(IV)-oxo complex

“…Accordingly, isolation of terminal late transition metal–oxo (LTMO) species to the right of group 8 (also known as the oxo wall for C 4v symmetry)141516 has only been achieved for heavy transition metals like iridium17 and platinum18 in ligand fields that are not tetragonal. Nevertheless, owing to their importance in a plethora of oxygen-dependent processes, inorganic compounds containing terminal metal–oxo moieties have been discussed or sought for this curious class of LTMOs19, which are thought to be reactive intermediates in a number of oxygen-dependent processes. Of particular relevance to this study are the cobalt(IV)–oxo species, which have also been proposed as reactive intermediates in a number of cobalt-mediated oxidation reactions2021222324252627.…”

“…However, Borovik and co-workers have suggested an alternative assignment for the former complex invoking a {Co III –OH–Sc 3+ } core33, thereby refuting the claim of the Co IV –O–Sc 3+ core. Thus, the existence of high-valent cobalt–oxo species and LTMOs is still controversial and remains elusive19.…”

Edelmetalle in Polyoxometallaten

“…Kürzlich durchgeführte relativistische DFT‐Rechnungen sagen chemische Verschiebungen und Linienbreiten im 17 O‐NMR‐Spektrum voraus, die stark von den experimentellen Daten abweichen, die dem terminalen Gold‐Oxo‐Liganden zugeschrieben wurden 19b. Die Autoren haben kürzlich die Originalveröffentlichungen zurückgezogen119 und berichten jetzt,120a dass die “Pt IV ‐ und Au III ‐Komplexe” lediglich Salze des lange bekannten 19‐Wolframato‐2‐phosphats [{WO(OH 2 }{PW 9 O 34 } 2 ] 14− sind,120b mit kristallographisch nicht‐detektierbaren, farbigen Pt‐ und Au‐Verunreinigungen, und dass der “Pd IV ‐Komplex” eine fehlgeordnete Form des Pd II ‐Derivats ist 108…”