Copper-gold clusters

Konopka, M., Rousseau, R., Stich, I. and Marx, D. (2004) Detaching Thiolates from Copper and Gold Clusters Which Bonds to Break Journal ofthe American Chemical Society, 126, 12103-12111. 

The Miocene stratigraphy in the Baguio District has been intruded by a series of Pliocene rocks. The homblende-phyric Mafic Dike Complex intruded the central part of the Baguio District at 4.5 - 4 Ma (Waters et al. submitted). The complex is characterized by dense clusters of coarsely hornblende phenocrystic dikes with evidence for multiple injections. Several Pliocene to Pleistocene dioritic intrusive complexes are associated with porphyry copper-gold mineralization in the Baguio district. The Black Mountain Intrusive Complex includes the Black Mountain quartz diorite and the Mexico Diorite, as well as andesite dykes that have yielded ages of between 3.14 and 2.78 Ma (Waters et al. submitted Sweet etal. 2008). Other Pliocene intrusive rocks... 

Perello, J.A., Fleming, J.A., O Kane, K.P., Burt, P.D., Clarke, G.A., Himes, M.D., Reeves, A.T. 1995. Porphyry copper-gold-molybdenum deposits in the Island Copper cluster, northern Vancouver Island, British Columbia. In Schroeter, T.G. (ed.). Porphyry Deposits of the Northwestern Cordillera of North America. Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 46, 214-238. 

Gold clusters adopt planar structures with larger numbers of atoms than silver and copper clusters, as demonstrated by combined experimental and theoretical studies . 

Nanosized cobalt, copper, gold, nickel, rhodium, and silver particles have been stabilized by polyions and polymers [514, 549-553]. Particularly significant has been the simultaneous reduction of HAuC14 and PdCl2 in the presence of poly(iV-vinyl-2-pyrrolidine) to give relatively uniform, 1.6-nm-diameter, palladium-coated gold bimetallic clusters [554]. 

Melnik and Parish (10) correlated 197Au Mossbauer and X-ray structural data for gold clusters in 1986, and Salter (11) has recently published a review of the stereochemical nonrigidity exhibited in solution by the metal skeletons of some mixed-metal clusters containing copper, silver, and gold. 

The excitation energies (38) are 1.39 eV, 3.75 eV and 1.14 eV for Cu, Ag and Au, respectively. Thus, we anticipate that DIM should be quite applicable to the study of silver clusters and should be of moderate applicability to the characterization of copper and gold clusters (see following discussions). 

Figure 4 Nanoclusters synthesized by irradiation of water solutions and stabilized by PVA. From left to right copper, stiver, and gold clusters. The colors ofultradivided metals are known from long. In the Middle Ages, they were produced in fused glasses under reducing conditions to produce stained glasses.

Such a reaction of Fe(CO)5 (at 293-363 K, PVP) without ultrasonic radiation proceeds very slowly and only after few days there, a material is formed with very low Fe content (2%, the isolated particles 2-5 nm in size). It is of interest that the sonochemical decomposition of Fe(CO)5 does not proceed in the presence of PVP if THF is used as the solvent, but the reaction is very effective when anisole is used as the solvent and PFO is used as the polymer matrix [93]. A black product formed contains up to 10% (in mass) of the spheric particles of nonoxidized Fe (mainly y-Fe, with little content of a-Fe) with 1-12 nm in size (the mean diameter is 3nm, as shown in Figure 3.7). It is likely that the big particles present the flocks of little ones ( 2-2.5nm). The sonochemical synthesis allows us to produce the functionalized amorphous nanoparticles of ferric oxide with 5-16 nm in diameter [94]. The ultrasonic irradiation in the PFO presence allows us to also produce the stabilized nanoparticles of copper, gold, and so on. In the literature the findings are not about the bimetallic particle formation in the ultrasonic fields by carbonyl metal reduction in the polymer matrices presence (as, for example, in the case of the carbon-supported Pt-Ru from PtRu5C(CO)i6 reduced clusters [95]). 

Figure 6.14 Fits between b3p85/St-RECP calculated (red), for (a) copper, (b) silver, and (c) gold clusters, and VB model estimated (blue) D /n values (kcalmoh ) as a function of cluster size. (Reproduced with permission from Figure 9 in Ref [2f].)...

Lower stability of palladium clusters compared to nickel and platinum ones is explained by lower energy of the Pd —Pd bond. It is assumed that the energy of a M — M bond can be measured by the energy of sublimation, which for Ni, Pd, and Pt is 427, 354, and 565 kJ mol respectively. For Cu, Ag, and Au, the energy of sublimation is 339, 285, and 364 kJ mol respectively. It turns out that in the case of group 11 metals, according to predictions, the number of silver clusters is smaller than that of copper and gold clusters. 

We may also use the concept of similarity functions in comparing the structures of the Ag clusters with those of other elements, i.e., with the structures of copper, nickel, and gold clusters. In order to eompare the structures, we have rescaled the structures according to the lattiee constants of the crystalline materials. The resulting similarity funetions... 

Whereas pure gold clusters Au are planar up to 12 constituent atoms (n = 12) [55], copper clusters have a clear-cut preference for 3D structures [56], The tendency is more pronounced in the scandium doped derivatives (Cu ySc) as scandium prefers a high coordination niunber. The inherent phenomenon is analyzed hereafter for CuigSc+ [57], Therefore, it comes as a surprise that the planar CU7SC is about 0.1 eV more stable than the 3D isomers. 

DFT is a powerful method for determining reaction mechanisms over metal-oxide systems. We have chosen to review studies that focus on developing catalysts for the water-gas-shift reaction because this is a particularly active research area with numerous examples of DFT application to supported metal-oxide catalysis. The studies first considered herein assess the activity of unsupported gold and copper metal clusters, which can then be compared directly to studies over the analogous oxide-supported systems. The importance of considering particle-support interactions is emphasized, because the oxide support can often play an active role in catalytic mechanisms. 

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