Synthesis and reactivity of dimethyl gold complexes supported on MgO: characterization by infrared and X-ray absorption spectroscopies

J. Guzman, B.G. Anderson, C.P. Vinod, K. Ramesh, J.W. Niemantsverdriet, B.C. Gates

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Abstract

Di-Me gold complexes bonded to partially dehydroxylated MgO powder calcined at 673 K were synthesized by adsorption of Au(CH3)2(acac) (acac is C5H7O2) from n-pentane soln. The synthesis and subsequent decompn. of the complexes by treatment in He or H2 were characterized with diffuse reflectance Fourier transform IR (DRIFT), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopies. The XANES results identify Au(III) in the supported complexes, and the EXAFS and DRIFTS data indicate mononuclear di-Me gold complexes as the predominant surface gold species, consistent with the lack of Au-Au contributions in the EXAFS spectrum and the presence of nas(CH3) and ns(CH3) bands in the IR spectrum. EXAFS data show that each complex is bonded to two oxygen atoms of the MgO surface at an Au-O distance of 2.16 .ANG.. The DRIFT spectra show that reaction of Au(CH3)2(acac) with MgO at room temp. also formed Mg(acac)2 and H(acac) species on the support. Treatment of the di-Me gold complexes in He or H2 at increasing temps. varying from 373 to 573 K removed CH3 ligands and caused aggregation forming zerovalent gold nanoclusters of increasing size, ultimately with an av. diam. of about 30 .ANG.. Anal. of the gas-phase products during the genesis of the gold clusters indicated formation of CH4 (consistent with removal of CH3 groups) and CO2 at 473-573 K, assocd. with decompn. of the org. ligands derived from acac species. O2 and CO2 were also formed in the decompn. of ubiquitous carbonates present on the surface of the MgO support. [on SciFinder (R)]
Original languageEnglish
Pages (from-to)3675-3683
JournalLangmuir
Volume21
Issue number8
DOIs
Publication statusPublished - 2005

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