Sulfur-Bridged Silver Clusters

Up to this composition, it is always possible to find a charge balancing between Ag + cations on the one hand, and and S R anions on the other hand. Assuming 

The structural determinations of these large clusters with nuclearities greater than 120 metal atoms proved problematic. For such clusters, the intensities of the reflections dropped off rather sharply above 20 40° (for MoKa radiation), and the structure refinement usually resulted in unsatisfactorily high R factors, with a high residual electron density close to heavy atoms within the cluster molecule. More satisfying R factors can only be obtained if this electron density can be modeled as disordered atoms which, on the other hand, complicates efforts to provide precise estimates of the molecular formulae. These effects may result from a range of factors  

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Another possible means of obtaining multinuclear sulfur-bridged silver clusters would be to react silver thiolates (AgSR) with carbon disulfide (Scheme 3.11). 

Scheme 3.10 Synthesis of various sulfur-bridged silver clusters by reactions of silver carboxylates with silylated sulfur compounds in the presence of tertiary phosphanes.

In the case of selenium-bridged copper clusters, it was found that there is a structural transition from molecular spherical structures towards cutouts of the bulk structure when the clusters reach 70 copper atoms. An analogous structural transformation has not yet been found in the case of sulfur-bridged silver clusters. For etample, the dication [Ag7oS2o(SPh)28(dppm)2o] in 94 shows a sheD-like sulfur substructure that consists of an inner Sg and an outer S40 polyhedron (Figure 3.73). 

Tetranuclear copper complexes have tetrahedral, square-planar, or butterfly structures. The compound Cu4 (Pr 0)2PS2 4 has a distorted tetrahedral skeleton of the metal atoms with one sulfur atom symmetrically bonded to two copper atoms, while the other sulfur atom forms a bond with the third copper atom. Copper and silver form many clusters containing alkyl and aryl ligands (See Chapter 4). The complex Cu4(CH2SiMe3)4, like Cu4 N(SiMe3)2 4, has a square-planar structure with bridging alkyl ligands. In the alkyl compound, in contrast to the amide one, there are Cu —Cu bonds. 

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