Alkanethiol-protected silver clusters of average diameter 4.0 ( 0.5 nm form single-phase superlattice solids, and their X-ray powder diffractograms have been fully indexed to single cubic unit cells. Whereas alkanethiols with five or more carbon atoms form superlattices, the corresponding cluster with four carbons yield only separated clusters. The superlattice solids can be recrystallized from nonpolar solvents. No such superlattices are seen for the corresponding gold clusters. The superlattice collapses upon heating, but the solid retains the structure even at 398 K, much above the melting point of crystalline alkanes and the corresponding self-assembled monolayer. In situ variable-temperature X-ray diffraction investigations did not show any solid-state phase transitions in the superlattice. Temperature-dependent infrared spectroscopy reveals the melting of the alkyl chain, and it is seen that the chain as a whole achieves rotational freedom prior to the collapse of the superlattice. Calorimetric investigations show distinct monolayer and superlattice melting transitions. The chemical nature of the cluster-molecule interaction is similar to that of the previously investigated gold and silver systems, as revealed by NMR, mass, infrared, and X-ray photoelectron spectroscopies and thermogravimetry analyses. Conductivity measurements clearly manifest the superlattice melting transition. Diffusion constants in solution measured by NMR show that the relative decrease in the diffusion constant with increasing monolayer chain length is smaller for silver than for gold, suggested to be a signature of intercluster interaction even in solution. Corroborative evidence is provided by the variable-temperature UV/vis investigations of the clusters.

by sublimation, giving colorless crystals having a melting point of 67 °C.Te[N(SIMe3)2]2 (2). The procedure for the preparation of 2 was identical with that of 1 except freshly sublimed TeCl4 was first dissolved in toluene before being added to an LiN(SiMe3)2/«-hexane solution at -78 °C. In a typical preparation using 1.10 g of LiN(SiMe3)2 (6.57 mmol) and 0.51 g of TeCl4 (1.89 mmol), a total of 0.43 g (0.97 mmol, 50% yield) of orange crystalline material having a melting point of [63][64][65] °C could be isolated by sublimation from the crude product. However, in order to obtain analytically pure product, the orange crystalline material had to be sublimed again twice (mp 69-71 °C). Anal. Found (calc

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Three new sulfides Li 2 CdSnS 4 (1), Na 2 CdSnS 4 (2) and Na 6 CdSn 4 S 12 (3), have been synthesized using a molten flux of alkali-metal polysulfides and structurally characterized by single crystal X-ray diffraction studies. Both the layered compound 1 and the three-dimensional compound 2 have tetrahedral anionic frameworks of (CdSnS 4 ) 2Ϫ and, for charge compensation, alkali-metal cations. The two-dimensional compound 3 has Na ϩ ions interleaved between anionic (CdSn 4 S 12 ) 6Ϫ layers with an octahedral framework. Compounds 1, 2 and 3 are structurally related to Cu 2 CdGeS 4 , LiAlSe 2 and Na 2 SnS 3 respectively. Compound 2, as determined from its diffuse reflectance spectrum, is a semiconductor with a band gap of 1.52 eV.

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The novel compounds Sr13NbAs11 and Eu13NbAs11 have been synthesized from SrAs, Eu5As4, Sr, Nb and As in niobium ampoules at 1173–1273 K. The tetragonal tI 200 phases are defect variants of the Ca14AlSb11 structure (space group I41/acd (no. 142); Sr13□NbAs11: a = 1649.8(2) and c = 2214.1(3); Eu13□NbAs11: a = 1632.9(8) and c = 2197.3(8) pm; Z = 8). The structures are built from the cations Sr2+, and Eu2+, respectively, and from the anions [NbAs4]7−, As3−, and the linear polyanion [As3]7−. This polyanion (isosteric to I3−) is asymmetric with d(AsAs) = 273.0 and 346.0 pm (Sr) and 274.7 and 335.6 pm (Eu), respectively. The bond lengths in the tetrahedral anions are d(NbAs) = 250.8 and 251.1 pm. The complete structural arrangement is related to that of Cu2O by forming two interpenetrating networks. The oxygen atoms are substituted by niobium centered As4 tetrahedra, and the Cu atoms are substituted by As6 octahedra (centered by Sr, Eu). The central As atoms of the polyanions connect the nets. Both As networks are enveloped by the remaining cations forming cubes, tetragonal antiprisms and capped trigonal prisms.