Co clusters

Hihara T, Pokrant S and Becker J A 1998 Magnetic moments and chemical bonding in isolated Bi Co clusters Chem. Phys. Lett. 294 357... 

A boron-containing Co cluster is formed by reacting EtjNBBrT with Tl[Co(CO)4] in benzene at RT ... 

Typical Mossbauer spectra for the fresh, reduced, carblded and used Fe/ZSM-5 system are shown in a composite Fig. 5. Similar spectra were obtained for the Fe-Co/ZSM-5 system. The product distribution for the F-T reaction, using the Fe and Fe-Co systems, are shown in Table 1. The gasoline range hydrocarbon yield increased from 75 to 94%, when the Fe-Co clusters were used in place of Fe only. In a typical CEMS (Conversion Electron Mossbauer Spectroscopy) of the Fe-Co system, no spectrum for 57pg vas observed even after one week from this. It was concluded that in the Fe-Co clusters Co was predominantly in the "mantle" and Fe species were In their "core," in the parlance of metallurgy/geophysics. This model Is sometimes referred to as the cherry model. 

Mixed-metal clusters are also accessible from Co2(CO)8. For example, the following reaction (Equation (2)) leads to a purple-black Au-Fe-Co cluster with a trigonal bipyramidal array of metals, via a long-known mixed Co-Fe red-brown colored cluster intermediate.79... 

The stability of phosphine-substituted Co clusters derived from Co4(CO)10(/r4-PPh)2 was examined under hydroformylation conditions using cylindrical internal reflectance (CIR) spectroscopy.148 [(CO)4Fe(//-PtBu2)Rh(CO)L], PPN[(CO)3CoO/-P(CMe3)2)Rh(CO)(HP(CMe3)2)], and... 

The ab initio SCF cluster wavefunction has been used to investigate the bonding of CO and CN- on Cu,0 (5,4,1), (5 surface layer, 4 second layer and 1 bottom layer atoms), and to calculate their field dependent vibrational frequency shifts in fields up to 5.2 x 107 V/cm(46). A schematic view of the Cu10 (5,4,l)CO cluster is shown in Figure 8. In order to assess the significance of Lambert s proposal, that the linear Stark effect is the dominant factor in the field dependent frequency shift, the effect of the field was calculated by three methods. One is by a fully variational approach (i.e., the adsorbate is allowed to relax under the influence of the applied field) in which the Hamiltonian for the cluster in a uniform electric field, F, is given by... 

Figure 8. A schematic view of the Cu10 (5,4,l)CO cluster. (Reprinted with permission from ref. 45b. Copyright 1985 American Institute of Physics.)...

The magnetic moments of Fe, Co, and Ni clusters with sizes up to 700 atoms have been measured by Billas et al.1,2 Those measurements were made under conditions where the clusters exhibit super-paramagnetic behavior for low cluster temperatures (vibrational temperature Tv b = 78 K for Ni and Co clusters and 120 K for Fe clusters). Their results are shown in Figure 1. As... 

Reactions of Ni38 with N2, Ft and CO Cluster Structure and Adsorbate Binding Sites. 

C02(CO)8 SiOj Adsorption from solution and thermal treatment under hydrogen High metal dispersion, small Co clusters favor alcohol formation in the CO hydrogenation [138]... 

Alumina-supported catalysts prepared using the bimetallic carbonyl precursors showed a better performance in alkene hydroformylation than conventional Co-Rh catalysts. This was related to the presence of highly dispersed Rh-Co clusters with frames corresponding to that of the parent carbonyl-precursor that were characterized by EXAFS [140, 183]. Silica-supported bimetallic entities RhCo3,... 

Stepanyuk et al. [471] have applied local approximation of the density-functional theory and the Korringa-Kohn-Rostoker (KKR) Green s function method to determine the energy of Co adatoms located at the ideal Au(lOO) surface. Total-energy calculations have shown that Co atoms and small Co clusters are preferably embedded inside the substrate. 

Indeed, eobalt and a promoter metal may form an integral metal particle deposited on the support oxide, altering the electronic properties of the surface cobalt metal atoms (Figure 4C). Depending on the promoter element added to the Co cluster, alloying might lead to an increased catalyst activity, selectivity, as well as stability. 

This section excludes the quite extensive dinuclear and polynuclear Os/CO cluster chemistry, which will only be referred to where it overlaps with classical coordination chemistry. The general classes of Os dimers that are often encountered are Os2n+ in = 4-8) complexes with Os—Os bonds, with or without bridging ligands Os(II) dimers,... 

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