Clusters preparation

Figure 6. Scale-drawn schematic of the cluster reactor in relation to the pulsed cluster source. The letters A-F indicate the various stages of cluster preparation or synthesis, cooling, mixing and reacting, and finally flowing into vacuum toward detection.

Substrate reactivity was as expected (Arl > ArBr ArCl). In contrast to the Suzuki cross-coupling, however, Cu and Ru clusters were not active in the Heck reactions, and the activity of Cu/Pd clusters was lower than that of pure Pd clusters. Note the higher activity of Pd clusters prepared in situ (row F) compared to pre-prepared clusters (rows B and G). This increased activity tallies with our findings for Suzuki cross-coupling (7). After reaction, palladium black was observed in all the vials in rows B and G, but not in row F. 

Harada M, Asakura K, Toshima N (1993) Catalytic activity and structural analysis of polymer-protected gold/palladium bimetallic clusters prepared by the successive reduction of hydrogen tetrachloroaurate(ffl) and palladium dichloride. J Phys Chem 97 5103-5114... 

SCHEME 5. Extended tetramannosylated clusters prepared by Touaibia et al.76... 

Fig. 13. Mannosylated prophyrin clusters prepared by Ballut et al. for liposome preparation.

Figure 6 Mo-Fe-S clusters prepared as the models of FeMo-co, representing the partial structures of FeMo-co...

Lu, P. et al., Polymer-protected Ni/Pd bimetallic nano-clusters preparation, characterization and catalysis for Hydrogenation of Nitrobenzene, J. Phys. Chem. B, 103, 9673, 1999. 

Toshima, N., Yonezawa, T., and Kushihashi, K., Polymer protected Pd-Pt bimetallic clusters preparation, catalytic properties and structural considerations, J. Chem. Soc. Faraday Trans., 89, 2537, 1993. 

Toshima, N., Takahashi, T., and Hirai, H., Polymerized micelle-protected platinum clusters-preparation and application to catalyst for visible light-induced hydrogen generation, J. Macromol. Sci. -Chem., A25, 669,1988. 

The concept of dynamic silver clusters capable to transfer between molecules was also pointed out recently by Ras et al. for silver clusters prepared by photoactivation using PM A A as scaffold [20], Every specific initial ratio of silver ions to methacrylate unit, Ag+ MAA, results in distinct spectral bands (Fig. 12a, b). Thus, an initial ratio 0.5 1 gives an absorption band at 503 nm, whereas a ratio 3 1 gives a band at 530 nm. The shuttle effect was proven when for a given silver cluster solution with ratio 3 1 and absorption at 530 nm, a blue shift was achieved by the addition of pure PMAA. For instance if the added amount of polymer decreases the ratio Ag+ MAA from 3 1 to 0.5 1, the new optical band will match exactly with the band corresponding to a solution with initial ratio 0.5 1, that is 503 nm (Fig. 12c). The explanation given for this blue shift was the redistribution of the existent silver clusters in PMAA chains over the newly available PMAA chains, in other words that the clusters shuttle from partly clusters-filled chains to empty ones. 

Fig. 12 (a) Image of PMAA-protected fluorescent silver clusters prepared with increasing initial ratio Ag+ MAA from 0.5 1 to 12 1 and equal irradiation time, (b) Absorption spectra of the same samples as in (a), (c) Variation of absorption maxima of some of the samples in (a) with molar ratio. Black arrows indicate how the absorption band shifts to the blue with the addition of extra polymer to a fluorescent cluster solution explaining the transfer effect of silver clusters among PMAA chains [20]... 

The ability to prepare well-defined intradendrimer metal nanoclusters depends strongly on the chemical composition of the dendrimer. Spectroscopic results, such as those shown in Fig. 7, indicate that when G4-NH2, rather than the hydroxyl-terminated dendrimers just described, is used as the template a maximum of 36 Cu + ions are sorbed most of these bind to the terminal primary amine groups. Reduction of a solution containing 0.6 mmol/1 CUSO4 and 0.05 mmol/1 G4-NH2 results in a clearly observable plasmon resonance band at 570 nm (Fig. 11) [122,124,125] which indicates that the Cu clusters prepared in this way are larger than 4 nm in diameter. This larger size is a consequence of ag-... 

This review will focus on the NMR properties of Zintl ion complexes, namely the solution properties of the ions where E = Si, Ge, Sn, Pb, and the products derived from those clusters. Closely related clusters prepared by other means, such as the recent, elegant organo polystannane work of Schnepf, Power, Huttner, and Fischer, are briefly mentioned but are not the focus of this review. Related overviews of dynamic organometallic complexes [1,2] and the stmcture and bonding of Zintl ions [3-5] can be found in previous reviews and in other chapters of this book. 

It has been shown that a variety of substituents can be attached to the outside of the group 14 Zintl ion clusters in exo positions (i.e., not vertex or interstitial positions) [70,73-78]. A variety of alkyl, aryl, and main group moieties have been attached to Ge9 and Sn9 clusters. The structures of these clusters are similar to some organos-tannane clusters prepared via different synthetic routes. This burgeoning class of compounds is rapidly developing however, little is known about the effect of the exo-substituents on the dynamic properties of the clusters. Only the RSng ions, where R = i-Pr, t-Bu, and SnCys, Sn- -Bu3, have been studied in detail [70]. 

Morula cell, 35 101 Mosaic spread, 47 471 [Mo,S4([9]aneN3),], structure, 37 154 Mo—S bridge, 38 55 M04S4 clusters, preparation, 38 26-27 [Mo,84] core, formation, 38 59 M04S4 cores... 

Wu SX, Zeng HX, Schelly ZA (2005) Growth of uncapped, subnanometer size gold clusters prepared via electroporation of vesicles. J Phys Chem B 109 18715-18718... 

Semiconductor clusters have traditionally been prepared by the use of colloids, micelles, polymers, crystalline hosts, and glasses. The clusters prepared by these methods have poorly-defined surfaces and a broad size distribution, which is detrimental to the properties of the semiconductor materials. The synthesis of monodisperse clusters with very well-defined surfaces is still a challenge to synthetic chemists. However, some recent approaches used to overcome these problems are (i) synthesis of the clusters within a porous host lattice (such as a zeolite) acting as a template and (ii) controlled fusion of clusters. 

No systematic synthesis of any cluster has been devised as yet. The only generalizable statement in cluster preparations is that clusters may be formed when a coordinative-ly unsaturated metal species is generated in the absence of donor ligands 231, 241). Consequently, clusters are often formed as unexpected products in reactions where the formation of unsaturated metal species is imaginable but not obvious. Whereas these obscure formations of clusters cannot be treated in this chapter, some preparative procedures used more often deserve comment. 

Di 3-phosphinidene) clusters, preparation, 6, 268 Diplatinum(O) complexes, preparation and characteristics,... 

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