Noble Metal Containing/Based POMs


Noble Metal Polyoxometalate Research
featured in Platinum Metals Review

Platinum Metals Rev., 2014, 58, (1), 40

Polyoxometalates (POMs, discrete nanosized metal oxo anions) are an increasingly fascinating object of study owing to their enormous structural diversity and unique combination of properties, such as thermal and oxidative stability, tunability of acidity and redox activity, and ability to activate easily accessible “green” oxidants (O2 and H2O2), thus making them attractive for applications in many different areas, for example, in catalysis, magnetism, nanotechnology, and medicine. Although this class of compounds was discovered as far back as 1826, until recently POMs were known predominantly for Group 5 and 6 addenda metals in high oxidation states (e.g. W6+, V5+).In 2008 we reported the synthesis, structure, and preliminary catalytic studies of [PdII13As8VO34(OH)6]8 (Pd13As8), the first member of a novel subclass of polyoxoanions built exclusively of d8 PdII addenda metal ions. All PdII ions in Pd13As8 retain square-planar coordination geometry, in sharp contrast to all other known discrete POMs, which generally contain metal centers in octahedral environments. Even more recently we have shown the possibility of preparing other hetero-13-palladate derivatives, in which the {AsO4}3- capping fragments in Pd13As8 are replaced by lone-pair-containing {SeIVO3}2- and organic-functionalized {PhAsVO3}2- groups. We also demonstrated the existence of another structural type of polyoxopalladate, [Pd15P10O50]20- (Pd15P10), which comprises 15 PdII addenda ions and adopts the shape of a star pentagon. We also discovered that the Pd12L8 heteropolypalladate shell in the above species can stabilize unusual coordination numbers and geometries for the encapsulated PdII ion, including unprecedented eight-fold cubic coordination. Wickleder et al. reported the solid-state d7 metal cluster anion [PtIII12O8(SO4)12]4-, which is composed of six dumbbell-shaped [Pt2]6+ ions linked by oxo and sulfate bridges.

There is great interest in soluble late-transition-metal oxo complexes as potential models of so-called MOx “suboxide clusters”, which have been proposed to be crucial intermediates in noble-metal-based heterogeneous catalytic oxidation systems. Furthermore, noble-metal-based materials are important as catalysts in numerous industrially relevant processes and devices, including low-temperature and environmentally benign O2-based oxidations, reforming, automobile converters, and fuel cells. This background warrants an extension of our polypalladate(II) work to other d8 metal ions (e.g. platinum(II), gold(III)).

Selected Publications

  • Polyoxometalates made of Gold: The Polyoxoaurate [AuIII4AsV4O20]8-
    Izarova, N. V.; Vankova, N.; Heine, T.; Ngo Biboum, R.; Keita, B.; Nadjo, L.; Kortz, U., Angew. Chem. Int. Ed. 2010, 49, 1886-1889. [Read Online]
  • Self-assembly of star-shaped heteropoly-15-palladate(II)
    Izarova, N. V.; Ngo Biboum, R.; Keita, B.; Mifsud, M.; Arends, I. W. C. E.; Jameson, G. B.; Kortz, U. Dalton Trans. 2009, 9385-9387. [Read Online]
  • Heteropoly-13-Palladates(II) [PdII13(AsVPh)8O32]6- and [PdII13SeIV8O32]6-
    Izarova, N. V.; Dickman, M. H.; Ngo Biboum, R.; Keita, B.; Nadjo, L.; Ramachandran, V; Dalal, N. S.; Kortz, U. Inorg. Chem. 2009, 48, 7504-7506. [Read Online]
  • The Palladium(II)-Decorated 22-Tungsto-2-Bismuthate(III), [Pd3(H2O)9Bi2W22O76]8-
    Bi, L.-H.; Dickman, M. H.; Kortz, U. CrystEngComm 2009, 11, 965-966. [Read Online]
  • Complete List of Publications

Noble Metal in Action

Ulrich Kortz, Chemistry professor at Jacobs University, and his team report the synthesis of a novel, discrete noble metal-oxide, containing a record number of 22 palladium atoms, as well as two central copper ions. In addition to its high catalytic potential, this {Cu2Pd22} cluster compound also exhibits very unusual intramolecular magnetic interactions. The study has now been published as a “Very Important Paper” in the Angewandte Chemie International Edition.