Cluster copper

Winter B J, Parks E K and Riley S J 1991 Copper clusters the interplay between electronic and geometrical structure J. Chem. Rhys. 94 8618... 

Cheshnovsky O, Taylor K J, Conceicao J and Smalley R E 1990 Ultraviolet photoeieotron spectra of mass-selected copper clusters evolution of the 3d band Phys. Rev. Lett. 64 1785... 

Quantum mechanical calculations electrochemical promotion, 267 with copper clusters, 268 with platinum clusters, 268 Quasi-reference electrodes, 118... 

Copper clusters containing two to four atoms have been formed (94) in argon and methane, whereas large, colloidal-copper particles resulted in dodecane matrices (94). The authors suggested that the "birth of the band structure of copper is clearly visible on passing from the dimer to the tetramer, with CU4 already possessing many of the features of the bulk metal (94). 

Fig. 28. The optical spectra of the products of the decomposition of CutiCiH, ) (A)-(C) wanned from 50 to 100 K from pure CjH< matrices (D)-(G) warmed from 45 to 70 K from concentrated CjH Ar = 1 10 matrices, showing the temperature-time evolution of "growing copper clusters in the size regime less than 1.0 nm (122).

Ruthenium-copper and osmium-copper clusters (21) are of particular interest because the components are immiscible in the bulk (32). Studies of the chemisorption and catalytic properties of the clusters suggested a structure in which the copper was present on the surface of the ruthenium or osmium (23,24). The clusters were dispersed on a silica carrier (21). They were prepared by wetting the silica with an aqueous solution of ruthenium and copper, or osmium and copper, salts. After a drying step, the metal salts on the silica were reduced to form the bimetallic clusters. The reduction was accomplished by heating the material in a stream of hydrogen. 

When the ruthenium EXAFS for the ruthenium-copper catalyst is compared with the EXAFS for a ruthenium reference catalyst containing no copper, it is found that they are not very different. This indicates that the environment about a ruthenium atom in the bimetallic catalyst is on the average not very different from that in the reference catalyst. This result is consistent with the view that a ruthenium-copper cluster consists of a central core of ruthenium atoms with the copper atoms present at the surface. 

If the degree of coverage of the ruthenium by the copper is very high, the copper atoms should be coordinated extensively to ruthenium atoms. It is emphasized that the ruthenium-copper clusters are of such a size (average diameter of 32A by electron microscopy (33)) that the surface metal atoms constitute almost half of the total. Hence for a Cu/Ru atomic ratio of one, the number of copper atoms would correspond roughly to that required to form a monolayer on the ruthenium. 

The copper EXAFS of the ruthenium-copper clusters might be expected to differ substantially from the copper EXAFS of a copper on silica catalyst, since the copper atoms have very different environments. This expectation is indeed borne out by experiment, as shown in Figure 2 by the plots of the function K x(K) vs. K at 100 K for the extended fine structure beyond the copper K edge for the ruthenium-copper catalyst and a copper on silica reference catalyst ( ). The difference is also evident from the Fourier transforms and first coordination shell inverse transforms in the middle and right-hand sections of Figure 2. The inverse transforms were taken over the range of distances 1.7 to 3.1A to isolate the contribution to EXAFS arising from the first coordination shell of metal atoms about a copper absorber atom. This shell consists of copper atoms alone in the copper catalyst and of both copper and ruthenium atoms in the ruthenium-copper catalyst. 

This discussion of EXAFS on ruthenium-copper clusters has emphasized qualitative aspects of the data analysis. A quantitative data analysis, yielding information on the various structural parameters of interest, has also been made and published (8). Of particular Interest was the finding that the average compo tion of the first coordination shell of ruthenium and copper atoms about a ruthenium atom was about 90% ruthenium, while that about a copper atom was about 50% ruthenium. Details of the methods Involved in the quantitative analysis of EXAFS data on bimetallic clusters can be obtained from our original papers (8.12-15). 

The results of the EXAFS studies on osmium-copper clusters lead to conclusions similar to those derived for ruthenium-copper clusters. That is, an osmium-copper cluster Is viewed as a central core of osmium atoms with the copper present at the surface. The results of the EXAFS investigations have provided excellent support for the conclusions deduced earlier (21,23,24) from studies of the chemisorption and catalytic properties of the clusters. Although copper is immiscible with both ruthenium and osmium in the bulk, it exhibits significant interaction with either metal at an interface. 

The ruthenium-copper and osmium-copper systems represent extreme cases in view of the very limited miscibility of either ruthenium or osmium with copper. It may also be noted that the crystal structure of ruthenium or osmium is different from that of copper, the former metals possessing the hep structure and the latter the fee structure. A system which is less extreme in these respects is the rhodium-copper system, since the components both possess the face centered cubic structure and also exhibit at least some miscibility at conditions of interest in catalysis. Recent EXAFS results from our group on rhodium-copper clusters (14) are similar to the earlier results on ruthenium-copper ( ) and osmium-copper (12) clusters, in that the rhodium atoms are coordinated predominantly to other rhodium atoms while the copper atoms are coordinated extensively to both copper and rhodium atoms. Also, we conclude that the copper concentrates in the surface of rhodium-copper clusters, as in the case of the ruthenium-copper and osmium-copper clusters. 

Since ruthenium and rhodium are neighboring elements in the periodic table, a closer comparison of the properties of ruthenium-copper and rhodium-copper clusters is of interest (17). When we compare EXAFS results on rhodium-copper and ruthenium-copper catalysts in which the Cu/Rh and Cu/Ru atomic ratios are both equal to one, we find some differences which can be related to the differences in miscibility of copper with ruthenium and rhodium. The extent of concentration of copper at the surface appears to be lower for the rhodium-copper clusters than for the ruthenium-copper clusters, as evidenced by the fact that rhodium exhibits a greater tendency than ruthenium to be coordinated to copper atoms in such clusters. The rhodium-copper clusters presumably contain some of the copper atoms in the interior of the clusters. 

The copper-copper interatomic distance in rhodium-copper clusters is substantially longer than in metallic copper (2.62-2.63A vs. 2.556A) and closer to the value (2.64A) obtained for the rhodium-... 

Knickelbein, M.B. (1992) Electronic shell structure in the ionization potentials of copper clusters. Chemical Physics Letters, 192, 129-134. 

In 1996 Stack and co-workers reported an unusual 3 1 (copper 02 stoichiometry) reaction between a mononuclear copper(I) complex of a A-permethylated (lR,2R)-cyclohexanediamine ligand with dioxygen. The end product of this reaction, stable at only low temperatures (X-ray structure at —40 °C) is a discrete, mixed-valence trinuclear copper cluster (1), with two Cu11 and a Cu111 center (Cu-Cu 2.641 and 2.704 A).27 Its spectroscopic and magnetic behavior were also investigated in detail. The relevance of this synthetic complex to the reduction of 02 at the trinuclear active sites of multicopper oxidases4-8 was discussed. Once formed, it exhibits moderate thermal stability, decomposed by a non-first-order process in about 3h at —10 °C. In the presence of trace water, the major isolated product was the bis(/i-hydroxo)dicopper(II) dimer (2). 

Figure 23. Plot of experimental ( ) and theoretical three-body rate constants as a function of cluster size for the clustering of one CO molecule to copper clusters, Cun. Note the dramatic increase in reactivity (almost four orders of magnitude) within the first seven atom additions to the clusters. The overall trend represents a transition from termolecular to effective bimolecular behavior. The solid line (theory) was obtained assuming a loose transition state while the dotted line shows the results for a tight transition state for monomer and dimer only (upper limit). Taken with permission from ref. 155.

Copper clusters, as reported by the Rice group(lc), do not react with hydrogen. Hydrogen chemisorption on copper surfaces is also an activated process. Surface beam scattering experiments place this barrier between 4-7 kcal/mole(33). This large value is consistent with the activated nature oT hydrogen chemisorption on metal clusters, and the trend toward bulk behavior for relatively small clusters (>25 atoms in size). 

Amino acid is one of the most important biological ligands. Researches on the coordination of metal-amino acid complexes will help us better understand the complicated behavior of the active site in a metal enzyme. Up to now many Ln-amino acid complexes [50] and 1 1 or 1 2 transition metal-amino acid complexes [51] with the structural motifs of mononuclear entity or chain have been synthesized. Recently, a series of polynuclear lanthanide clusters with amino acid as a ligand were reported (most of them display a Ln404-cubane structural motif) [52]. It is also well known that amino acids are useful ligands for the construction of polynuclear copper clusters [53-56], Several studies on polynuclear transition metal clusters with amino acids as ligands, such as [C03] [57,58], [Co2Pt2] [59], [Zn6] [60], and [Fe ] [61] were also reported. 

Figure 1. (a) A schematic representation of the overall organization of the molecule of human ceruloplasmin. Domains 2,4, and 6 contain mononuclear copper centers, while the trinuclear copper cluster is located at the interface of domains 1 and 6. (b) An a-carbon ribbon diagram of the human ceruloplasmin molecule viewed along the pseudo threefold axis highlighting the triplication of the structure. Domains 1, 3, and 5 are depicted by striped motifs, whereas domains 2, 4, and 6 are dark shaded. The copper... 

In the elucidation of the X-ray structure of hCP by the method of isomorphous replacement, gold and mercury heavy atom derivatives were utilized. In the case of the mercury derivative, p-chloromercury-benzoate, the heavy atom bound to the free sulphydryl residue, C221, but for the gold cyanide derivative the gold atom was found to bind in the vicinity of the trinuclear copper cluster. A realistic explanation of this... 

The Cu+ ion and the copper cluster cations were more reactive than the similar silver cations. Methanol was unreactive to Cu and Ag (n = 1-5). Ethanol was unreactive to CU5 and Ag+ (n = 3-5). The general reactions are shown as equations with examples given after the equation (see Eqs. 44-48). 

Ruthenium compounds, 19 637-641 synthesis of, 19 640 uses for, 19 640—641 Ruthenium-copper clusters, 16 70 Ruthenium initiators, 26 934 Ruthenium plating, 9 823 Ruthenium-silica... 

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. 

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