Spectroscopic Study of Platinum and Rhodium Dendrimer (PAMAM G4OH) Compounds: Structure and Stability

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• 作者：Yuri Borodko ; Christopher M. Thompson ; Wenyu Huang ; Huseyin B. Yildiz ; Heinz Frei ; Gabor A. Somorjai
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：March 24, 2011
• 年：2011
• 卷：115
• 期：11
• 页码：4757-4767
• 全文大小：1336K
• 年卷期：v.115,no.11(March 24, 2011)
• ISSN：1932-7455

文摘

Hydroxyl-terminated, poly(amidoamine) (PAMAM) dendrimer-capped platinum and rhodium nanoparticles were studied with UV鈭抳is, Fourier transform IR, and UV-Raman spectroscopy. The adsorption bands in the region of 190鈭?00 nm were shown to be sensitive to the electronic structure of Pt compounds in solution and in the solid state. The electron charge-transfer Pt²⁺ 鈫?N band at 260 nm was attributed to mononuclear Pt²⁺ compounds, and resonance Raman (244 nm) established that the electron donors are amide nitrogen atoms. Multidentate coordination bonding with Pt²⁺ causes a strong stabilizing chelate effect, and this entropic factor hinders reduction of Pt²⁺ by BH₄^{鈭?/sup>. UV diffuse-reflectance spectra showed the appearance of new bands at 300 and 342 nm in PtG4OH deposited on mesoporous silica (SBA-15) induced by heating under reducing conditions. The new bands can be assigned to platinum clusters like binuclear Pt2+鈭扨t2+ and higher, dendrimer-capped analogs of platinum blue compounds. In the temperature range of 30 to 350 掳C, the decomposition of G4OH begins above 150 掳C with dehydrogenation of backbone. The presence of platinum and rhodium particles decreased the initial temperature of decay. In reducing conditions, the PtG4OH undergoes rearrangements of its secondary structure due to the formation of metallic platinum clusters. UV- photochemical degradation of G4OH, Pt- and Rh-dendrimer systems in ozone-rich atmosphere as well in H₂ and Ar showed that effect of UV light is greater than the of ozone. The ratio of initial rates for photolysis and 鈥渄ark鈥?ozonolysis was W_hv/W_O3 40.}