Price Ryan C, Whetten Robert L
Department of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
J Phys Chem B. 2006 Nov 9;110(44):22166-71. doi: 10.1021/jp062840r.
Near-infrared (1064-nm) irradiation of neat solid samples of benzenethiolate monolayer-protected gold clusters (MPCs) yields strong, well-resolved Raman spectra of the thiolate groups, comparable to those obtained for the same groups adsorbed at roughened gold electrodes. These clusters are formulated as TOAZ[AuN(SPh)M]Z-, N >> M and Z = 3-6, with core diameters of 1.7 and 1.5 nm, and were characterized previously by X-ray scattering, mass spectrometry, infrared spectroscopy, optical spectroscopy, nuclear magnetic resonance, and elemental analysis [Price, R. C.; Whetten, R. L. J. Am. Chem. Soc. 2005]. Numerous previous attempts to obtain spectra on various MPCs yielded only diffuse luminescence bands, as did benzenethiolate MPC samples of TOA2[Au44(SPh)28]2-, with 1.1-nm core diameters. The clusters are free of excess tetraoctylammonium bromide (TOABr) from the synthetic procedure, containing only the necessary TOA+ to maintain charge balance. In situ thermometry, using the anti-Stokes/Stokes intensity ratios, indicated the sample temperature remained below the onset of thermal decomposition. The Raman spectra of the clusters bear a strong resemblance to those obtained for nonmetallic (Au(I)SPh)x polymer samples that are not in resonant absorption at the laser wavelength. The smaller of the two cores, nominally TOA6[Au110(SPh)62], shows clearly a band at 505 cm(-1) assigned to a S-S stretch, suggestive of a moiety resembling diphenyl disulfide on the cluster surface. These results are interpreted with reference to recent reports suggesting a substantial "reconstruction" of the outermost gold layer upon thiolate adsorption (SAM formation).
对苯硫醇单层保护金簇（MPCs）的纯固体样品进行近红外（1064 nm）辐照，可得到硫醇盐基团的强且分辨率良好的拉曼光谱，与在粗糙金电极上吸附的相同基团所获得的光谱相当。这些簇被表示为TOAZ[AuN(SPh)M]Z-，N >> M且Z = 3 - 6，核心直径为1.7和1.5 nm，之前已通过X射线散射、质谱、红外光谱、光学光谱、核磁共振和元素分析进行了表征[普赖斯，R. C.；惠滕，R. L.《美国化学会志》2005年]。此前许多获取各种MPCs光谱的尝试仅产生了漫射发光带，直径为1.1 nm核心的TOA2[Au44(SPh)28]2-的苯硫醇盐MPC样品也是如此。这些簇在合成过程中不含过量的四辛基溴化铵（TOABr），仅含有维持电荷平衡所需的TOA+。使用反斯托克斯/斯托克斯强度比进行的原位测温表明，样品温度保持在热分解起始温度以下。这些簇的拉曼光谱与在激光波长下不处于共振吸收的非金属（Au(I)SPh）x聚合物样品所获得的光谱非常相似。两个核心中较小的那个，标称TOA6[Au110(SPh)62]，在505 cm(-1)处清晰显示出一个归属于S - S伸缩振动的峰，这表明簇表面存在类似二苯基二硫化物的部分。这些结果参考了最近的报告进行解释，这些报告表明硫醇盐吸附（自组装单分子层形成）后最外层金层会发生大量“重构”。
