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Bismuth−Palladium Heterometallic Carboxylate as a Single-Source Precursor for the Carbon-Supported Pd−Bi/C Catalysts

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posted on 06.07.2009, 00:00 by Bo Li, Haitao Zhang, Lan Huynh, Chantal Diverchy, Sophie Hermans, Michel Devillers, Evgeny V. Dikarev
The heterometallic complex [Bi2Pd2(O2CCF3)10(HO2CCF3)2] (1) was obtained by the solid state reaction of BiIII trifluoroacetate/trifluoroacetic acid adduct with unsolvated trinuclear PdII trifluoroacetate. The crystal structure of 1 consists of discrete tetranuclear molecules, in which two paddlewheel [BiPd(O2CCF3)4] units are connected by two chelating-bridging trifluoroacetate ligands through bismuth ends. There are no metal−metal bonds in the tetrameric structure of 1, since both Bi···Pd (3.0843(4) Å) and Bi···Bi (4.5074(4) Å) distances are too long to be considered as bonding interactions. A study of the solution behavior revealed that not only the coordinated trifluoroacetic acid in 1 can be effectively replaced by other donor solvent molecules but also the tetranuclear complex can be cleaved in solution into discrete dinuclear Bi−Pd species. Complex 1 was used as precursor for the preparation of a bimetallic Pd−Bi carbon-supported catalyst. The preparation procedure included the modification of the carbon support to increase the number of oxygenated functions at its surface followed by grafting complex 1 via ligand exchange for surface carboxylates and activating thermally. The resulting catalyst, consisting of small supported metallic particles, was found to be more active than the reference materials prepared from multisource homometallic Pd and Bi precursors.