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In order to expand the range of high-quality nanosized semiconductor materials that can be obtained as quantum dots through a wet chemical route a series of oxidize-stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4nm has been prepared in aqueous solution using 2-mercaptoethanol and 1 -thioglycerol as stabilizers. It has been investigated by means of UV-vis absorption and photoluminescence spectroscopy, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive x-ray analysis (EDX).

A simple preparation of Cd(17)S(4)(SCH(2)CH(2)OH)(26) clusters in aqueous solution leads to the formation of colorless blocky crystals. X-ray structure determinations revealed a superlattice framework built up of covalently linked clusters. This superlattice is best described as two enlarged and interlaced diamond or zinc blende lattices. Because both the superlattice and the clusters display the same structural features, the crystal structure resembles the self-similarities known from fractal geometry. The optical spectrum of the cluster solution displays a sharp transition around 290 nanometers with a large absorption coefficient ( approximately 84,000 per molar per centimeter).

During the last decade the physical and chemical properties of semiconductor nanoclusters have been intensively investigated.'-4 Thereby the advances in this research field were strongly determined by the progress in the synthesis of monodisperse and well-characterized samples. Undoubtedly the most remarkable results in this context have been the crystallization of single-sized nanoclusters in three-dimensional superlattices which, however, succeeded only in a very few extraordinary cases like [Cd&(SPh) I 614? [Cd 17S4(SPh)28]~-,~ Cd 1 &(SCH2-C H Z O H )~~,~ and Cd32!314(SPh)36*4DMF.~ It is, therefore, a major goal to find new synthetic routes to enlarge the number of species in this novel class of materials. Especially the variation of cluster ligands and cluster sizes makes possible the control of the superlattice parameters and should give access to explanations of how collective phenomena arise by cluster-cluster interaction.We describe here the crystallization of Cd32S ld(SCH2CH-(OH)CH3)36*4H20 clusters and will discuss structural and optical properties. The preparation of the raw cluster sample was carried out analogously to sample d in ref 9 except using 1 -mercapto-2-propanol instead of 1 -thioglycerol."' During dialysis precipitation occurred as the pH value of the alkaline cluster solution decreased and colorless prismatic crystals of approximately 150 pm edge length were obtained. These crystals were no longer soluble in water, but dissolved readily in N,N-dimethylformamide (DMF). For X-ray analysis one single crystal was encapsulated in a capillary containing a few microliters of mother liquor because the crystals were found to crack during drying. Cracking also occurred below 0 OC, making low-temperature measurements impossible. Due to Katsikas, L.: Giersig. M.; Chemseddine. A.; Diesner, K.; Popovic, I. G.; Eychmiiller. A.; Weller, H. J . P h~s .Chum. 1994, 98, 7665.(IO) Briefly, a solution of 1.97 g (4.70 mmol) of Cd(C104)y6H20 and 1.0 mL ( 1 1.39 mmol) of I-mercapto-2-propanol in 250 mL of water was adjusted to pH 11.2 with 1 M NaOH before the addition of SO mL (2.04 mmol) of H2S with vigorous stirring. The transparent solution was heated to I00 "C until the UV/vis absorption spectrum displayed a transition at about 325 nm, similar to that shown in Figure 3. After cooling to room temperature, the crude cluster solution was dialyzed exhaustively against deionized water (using SpectrdPor MWCO 6-8000 dialysis tubings). 0002-786319511517-12881$09.00/0 Figure 1. Structure of a C~I~S I~( S C H~C H ( O H ) C H I ) V , *~H~O cluster. For clarity the organic residues have been omitted, but their orientations are indicated by the bonds that protrude from the thiolate S atoms to the corresponding first C atom. The four 0 atoms at the vertices form a slightly distorted tetrahedron (edge lengths, approximately 18.5 A). Bond lengths in A: Cd-S, 2.49( 1)-2.54( 1); Cd-SR, 2.46(2)-2.W I); Cd-0. 2.32( 1)-2.33 I). The cluster contains a 3-fold axis which coincides with that of the space group R3.these difficulties, t...

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