Tin clusters

TABLE 15. Redox peak potentials of several germanium and tin clusters, in THF, 0.1 M TBAP, working electrode graphite, counterelectrode Pt wire183... 

Ga3R3]2- (R = bulky aryl group) [24], isoelectronic with the aromatic cyclo-propenium cation. In addition, tin clusters exhibit a variety of interesting cage structures (see Chapter 2.5.4) [25]. 

The (TiN) + clusters produced by a laser-induced plasma reactor source were investigated by means of time-of-flight mass spectrometry. The mass spectral abundance indicates that the clusters have cubic structures resembling subunits of the fee lattice of TiN. The primary stoichiometries observed are (TiN) + (n = 1-126), except for Ti N , (n = 14, 63) (36). 

The structures of both the phenyl and 2,5-dimethylphenyl tin clusters were established by single-crystal X-ray diffraction. Under similar conditions, toluene was stannylated to produce a mixture of organotin compounds. Bromination of this mixture yielded 3-bromotoluene and 4-bromotoluene in a 2 1 ratio, with trace amounts of 2-bromotoluene. Similarly, PhBr was produced upon treatment of the phenyltin product with aqueous Br2. No applications of the stannylation reactions have yet been reported. 

The largest tin clusters known to date are the pair of isoleptic amido complexes [SnisZg] (Z = N(2,6-IPr2CeH3)(SiMe2X) X = Me, Ph). Both... 

FIGURE 39. Schematic representation of the hexanuclear tin cluster calculated in Reference 160... 

Transition metal-tin clusters can be formed from similar reactions and K2[Fe3S(CO)9] mixed with Me2SnBr2 resulted in the formation of a double-bridged cluster 75. Similarly,... 

For the condensation complexes of salicylaldoxime and di-n-butyltin oxide, the 2D H- Sn HMQC experiments proved to be especially powerful for the structural characterization of the different tin clusters existing in solution. Indeed, the numerous long-range correlation peaks (up to five bonds) observed in the 2D spectra allowed one to propose a structure for each of the species. Furthermore, our results clearly evidence that weak scalar couplings through coordinative N->Sn and O- Sn bonds can be observed. 

The effect of catalyst composition on the selectivity to the desired CDE is remarkable. It is clear that monometallic cluster catalysts almost completely hydrogenate CDT to CDA, whereas all three bimetallic clusters (RuSn, RhSn, and PtSn ) exhibit high selectivity toward CDE at approximately the same CDT conversion (50-75%). Pure tin clusters derived from Ph SnH are poor catalysts both in terms of activity and selectivity (conversion less than 10%). 

Since these homopolyatomic ZiniD anions and cations are devoid of ligands, they are sometimes referred to as naked" clusters. In general there is a good correlation between electronic structure and geometry as predicted by Wade s rules for the.se clusters, though some exceptions are known. Thus whereas Sn " and Bi are isoelectronic. they have different structures, the latter violating the rules. Only a small distortion of the bismuth cation, however, would convert it to the geometry ob.served for the tin cluster. 

The most stable clusters of tin, as well as of the rest of the elements in this group except carbon, are, by far, the nine-atom clusters. As mentioned above, Sng was the first deltahedral cluster to be structurally characterized. While Geg was added very soon after, nine-atom clusters of lead and silicon were found respectively 20 and 30 years later. ° Thus, the following discussion of geometry, charges, cluster-bonding, and electronic structure is valid not only for tin clusters, but also for those of silicon, germanium, and lead. 

Figure 2.6.11 The two types of capping observed for centered tin clusters the path (a) (b)->-(c) represents capping of a triangular base of the tricapped trigonal prismatic cluster the path (a) (d)->-(e) represents capping of the open pseudo-square face of the cluster as observed also for empty clusters (Figure 2.6.7). The capped triangular base in (b) opens up upon insertion of the capping atom towards the center of the cluster, in order to interact with the central atom, and this results in the cluster shown in (c)...

---