Gold(I) carboxylates and [Au(C(NH2)2(=S))2][SO3Me] for the deposition of gold and gold-doped SiOX materials by the atmospheric pressure combustion CVD process

Abstract

Complexes [AuO2CCH2OMe(PR3)] (3a, R = Et; 3b, R = nBu) were prepared by the reaction of [AuCl(PR3)] (1a, R = Et; 1b, R = nBu) with [AgO2CCH2OMe] (2), while [Au(C(NH2)2(=S))2][SO3Me] (4) was synthesized by electrolysis of Au in presence of thiourea in an aqueous solution of methanesulfonic acid. The thermal behavior of 3a,b and 4 was investigated by thermogravimetry (TG), displaying that 3a,b decompose in a single step, which contrasts the three-step decomposition of 4. TG-MS coupled experiments (MS = mass-spectrometry) were performed with 3b, proving that at first decarboxylation occurs, which is evidenced by the detection of CO2+. Complexes 3a,b and 4 were applied as CCVD (combustion chemical vapor deposition) precursors for the formation of gold deposits and gold-doped SiOx materials in presence of hexamethyldisiloxane (HMDSO) on silicon and glass substrates. In the combined depositions of gold and SiOx, 3a,b gave a granulated surface morphology, whereby samples deposited from 4 and HMDSO showed a porous structure as evidenced by SEM (scanning electron microscopy). The gold deposits exhibit separated particles at the substrate surface, whereof the sample deposited from 4 showed the highest amount of gold (3a,b, 3.8 at-% Au; 4, 13.3 at-% Au) as proven by XPS (X-ray photoelectron spectroscopy). The Au content of the appropriate SiOx:Au materials amounts to 1.2 at-%. XPS detail spectra of the Au 4f peaks confirm the predominant formation of Au(0) next to Au2O3. XPS depth profile measurements of the SiOx:Au samples confirmed a higher gold content when precursor 4 was applied instead of 3a,b. The as-deposited samples were used in heterogeneous catalysis for the reduction of 4-nitrophenol to 4-aminophenol with NaBH4, whereby the ones deposited from 4 (with and without a SiOx matrix) show the highest catalytic activity.