Formation processes of CdS ultrasmall particles from cadmium complexes of 2-mercaptoethanol (RSH) were investigated by means of stopped-flow and NMR spectroscopies. Two different initial processes depending on the amount of RS" ions have been found. The presence of S4Cdm(SR)i2 clusters in solution was observed by NMR spectroscopy. Formation of [S4Cdn(SR)24]2+ clusters having a 290-nm absorption peak was suggested. The correlation between the absorption peak and the diameter for polynuclear Cd2+-SR" complexes is expressed with the finite-depth quantum well model for ultrasmall particles. Electronic interaction between the capping agent and particle framework was suggested on the basis of the differences observed in the absorption wavelengths of the CdS-RSH clusters and the corresponding CdS-thiophenol clusters.Ultrasmall semiconductor particles whose diameters are a few nanometers have been paid special attention because of their unique size-dependent properties, such as optical and physicochemical properties.1-3 These properties are affected not only

Growing steps of CdS clusters in aqueous solution containing HOCH 2CH2 SH (2-mercaptoethanol, RSH) was investigated by means of stopped flow optical spectroscopy and proton NMR spectroscopy. When the amount of RS − was 4 times larger than Cd 2+ ions at alkaline pH, the growing cluster showed the change in the absorption peak via 242, 260, 280, 308, and 315 nm. Initial three peaks were assigned to [ Cd 1( SR )4]2−, [ S 1 Cd 4(SR)12]6−, and [ S 1 Cd 8( SR )16]2−, respectively. Among them, the cluster at 280 nm was very stable, comparable with the reported thiophenolate cluster [ S 1 Cd 8( SPh )16]2−. The relationship between the size and the absorption maximum for ultrasmall CdS particles reported was continuous to that obtained for the clusters in the present study.

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