Edelmetall (Pd, Pt und Au)-haltige Polyoxometallate
Zusammenfassung der Projektergebnisse
Polyoxometalates containing noble metals attract considerable attention in the last years, mainly due to their potential application as catalysts for various chemical processes ranging from low-temperature O2-based oxidations to water splitting. Within the current project we aimed to develop a young area of polyoxoanions built up exclusively by square-planar noble metal ions, such as PdII, PtII and AuIII. The first member of the noble metalates family, [Pd13O8(AsO4)8H6]8−, was reported just five years ago and only a handful number of other discrete polynuclear PdII oxocomplexes as well as a polyoxoaurate have been known to the moment the project starts. In sharp contrast to conventional polyoxometalates, built mainly by W VI, MoVI/V, VV, NbV ions in octahedral coordination geometry, polyoxopalladates and aurates have external heterogroups that appear to terminate the condensation process and allow the isolation of discrete species. Our systematic studies on condensation of PdII and AuIII aqua and hydroxo complexes in aqueous media allowed significantly deepen current knowledge about noble metal-based polyanions, the main principles of their formation and the main structural units of such species. Currently more than 40 polyoxopalladates with various structures and composition are known. In particular we have found out that the cuboid heteropolypalladate shell {PdII12O8(LXO3)8} in [Mz+PdII12O8(LXO3)8]n- polyanions represents a unique assembly allowing d-block metal ions Mz+ to exist in a highly unusual cubic crystal field, and as a result could generate unconventional electronic and magnetic properties. The polyoxopalladate anion [CuII2PdII22P12O60(OH)8]20- possessing a double-cuboid structure and containing two distant CuII centers showed very interesting magnetic behaviour that was highlighted at the University web-page (https://www.jacobs-university.de/node/15541). We were also able to prepare another POM based on AuIII ions as well as to synthesize a mixed palladate-aurate [NaAu4Pd8O8(AsO4)8]11- species. At the same time preparation of polyoxoplatinates appeared to be a much more complicated task because of a chemical inertness of PtII/III/IV ions and their tendency to form insoluble PtOxHy species with polymeric structures much faster than react with different heterogroups at the studied conditions. This required a shift from the initial project goal to the area of Pt-containing polyoxotungstates to investigate the reactivity of Pt ions in different oxidation states towards robust fully inorganic O-donor ligands. We were able to isolate a number of novel PtII, PtIII and PtIV complexes with monolacunary Keggin-type phosphotungstate, including the first ever PtIII containing polyoxotungstate [PtIII2(CH3COO)2(PW 11O39)Cl2]5-. Also several PdII-containing polyoxoanions were synthesized at the initial step as the model for PtII compounds. This study allowed to specify possible Pt precursors and necessary conditions which will help to prepare polyoxoplatinates in the future. We have also tested solid state 195Pt MAS NMR spectroscopy as an analytical tool for the analysis of Pt-containing polyanions which would be especially useful for characterization of solution unstable substances and the systems with possible Pt / W disorder. Solution stability, electrochemical and magnetic properties of the obtained compounds have also been investigated. For some of the species the possibility to act as electrocatalysts and precatalysits for various chemical processes has been shown. We believe the work performed in the framework of this project created an important basis for the future applications of these species, not only in the area of catalysis but also in other research fields, for example as precursors for small mono-sized nanoparticles in the supramolecular and solid-state systems; and there is no doubt that we will witness a further progress of the area of noble metal-based polyoxometalates chemistry in the future.
Projektbezogene Publikationen (Auswahl)
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Noble Metalate Bowl: The Polyoxo-6-Vanado(V)-7-Palladate(II) [Pd7V6O24(OH)2]6-. Angew. Chem. Int. Ed. 2010, 49, 7807-7811
N. V. Izarova, N. Vankova, A. Banerjee, G. B. Jameson, T. Heine, and U. Kortz
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Synthesis and Characterization of the Di-Copper(II)-Containing 22-Palladate(II), [CuII2PdII22PV12O60(OH)8]20-. Angew. Chem. Int. Ed. 2011, 50, 2639-2642
M. Barsukova-Stuckart, N. V. Izarova, G. B. Jameson, V. Ramachandran, Z. Wang, J. van Tol, N. S. Dalal, R. Ngo Biboum, B. Keita, L. Nadjo, and U. Kortz
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Polyoxopalladates Encapsulating 8-Coordinated Metal Ions, [MO8PdII12L8]n- (M = ScIII, MnII, FeIII, CoII, NiII, CuII, ZnII, LuIII; L = PhAsO32-, PhPO32-, SeO32-) Inorg. Chem. 2012, 51, 13214-13228
M. Barsukova-Stuckart, N. V. Izarova, R. A. Barret, Z. Wang, J. Van Tol, H. W. Kroto, N. S. Dalal, P. Jiménez-Lozano, J. J. Carbó, J. M. Poblet, M. S. von Gernler, T. Drewello, P. de Oliveira, B. Keita, U. Kortz
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The Selenite-capped Polyoxo-4-aurate(III), [AuIII4O4(SeIVO3)4]4-. Chem. Commun. 2012, 48, 9849-9851
Y. Xiang, N. V. Izarova, F. Schinle, O. Hampe, B. Keita, U. Kortz
