Cluster geometries cobalt

Tetranuclear alkyne clusters involving cobalt can adopt a variety of geometries. Reductive dehalogenation of ( Bu)(PhC=C)PCI by [Co2(CO)8] affords 39 in which a chain of four cobalt centers is supported by the functionalized alkyne, as shown in Eq, (15).146-147... 

The majority of tetranuclear alkyne clusters containing cobalt adopt butterfly geometries.151152 This is illustrated by the molecular structure of [Co4(/L4-r72-HC2H)(/L-CO)2(CO)8] (Fig. 16), which can be prepared by the... 

Cobalt offers many possibilities of cluster-core-geometry, but the chemistry of cobalt clusters is limited, again due to the weakness of first row metal-metal bonds and their susceptibihty to nucleophilic cleavage. Only in case of the methinyl tricobalt enneacarbonyls has a singular chemistry been developed, and therefore these compounds will be treated under a separate heading. 

A number of novel products have been isolated from the reaction of [B Hg]- [31426-87-6] and CoCl and [C HJ in THF (162,163). The predominant product is /< -2-(CpCo)-B4H8 [43061-99-0]. Also obtained are isomeric clusters containing up to four cobalt atoms, eg, (t]5-C5H5Co)4B4H8 [59370-82-0]. Characterization of these clusters indicate an unusual 2n framework electron count having geometries reminiscent of stricdy metallic clusters (11,164). 

Fig. 12. Schematic diagram of metal binding by human CCS. hCCS domains 1, 2, and 3 are labeled with roman numerals. Cysteine residues are designated as S. The disulfide bond in domain 2 is indicated by S-S. (a) Cobalt binding to hCCS. Electronic absorption spectra indicate that two equivalents of Co(II) bind per hCCS monomer, one through three or four cysteine residues in a tetrahedral geometry, and one with a geometry similar to that found in the zinc site of SODl (see text) (Zhu et al., 2000). (b) Copper binding to hCCS. XAS indicates that two Cu(I) ions bind per hCCS monomer in a sulfur-only liganding environment, with an additional heavy atom scatterer peak suggesting the presence of a /t2-bridged dicopper cluster (Eisses et al., 2000).

To clarify the mechanism of propylene adsorption on Ru-Co clusters the quantum-chemical calculation of interaction between it and Ru-Co, Ru-Ru, and Co-Co clusters were carried out. During the calculation it was assumed that carbon atoms of C-C bond are situated parallel to metal-metal bond. The distance at which the cluster and absorbable molecule begin to interact is characterized by the nature of active center. Full optimization of C3H6 molecule geometry confirms that propylene adsorbs associatively on Co-Co cluster and forms Jt-type complex. In other cases the dissociate adsorption of propylene is occurred. The presence of Ru atom provides significant electron density transfer from olefin molecule orbitals to d-orbitals of ruthenium in bimetallic Ru-Co- or monometallic Ru-Ru-clasters (independently on either the tertiary carbon atom is located on ruthenium or cobalt atom.). At the same time the olefin C-C bond loosens substantially down to their break. 

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