Surface interaction with metal center

An interesting oxycarbonyl cluster has been isolated in the reaction of 0s04 with CO under pressure. This was an intermediate in the preparation of the Os3(CO)i2. The X-ray analysis has established this as a cubane structure, with an oxygen bridging the four faces of the osmium tetrahedron. The Os-Os distance is 3.20 A and implies no bonding between the osmium centers. This molecule is of obvious interest as a potential model in the studies of carbon monoxide interaction with metal oxides and also metal surfaces, when the formation of metal oxides occurs (200). 

The arguments behind the d band model are quite general and should apply to the interactions in the transition state as well as in the initial and final (adsorbed) states of the process. We therefore expect correlations between the d band center and transition state energies to be the same as for chemisorption energies. This is illustrated in the bottom panel of Figure 4.10. Figure 4.16 shows in detail how the activation energy for methane on different Ni surfaces scales with the center of the d bands projected onto the appropriate metal states to which the transition state couples. 

Fig. 7 Crystal structures of proteins that interact with metal minerals, a iron-oxide clusters on the interior surface of DpsA, b close up view of the nucleation center 11, c tii Hf-oxo cluster, and d penta Hf-oxo cluster at the di-tyrosyl nucleation motif of fenic-ion-binding protein, Fbp. e cluster at an intersection of subunits in MoAVSto protein...

The effect of addition of AcOH in the hydrogenation mixture with Pt-catalyst modified with both DHCnd and DHVin can be explained by interaction of the basic center N- (region A) with the substrate molecule. The indole ring (in DHVin) and quinoline ring (in Cnd) (region B) are responsible for the coordination of the modifiers with metal centers on the surface of the catalyst. 

Besides electronic effects, structure sensitivity phenomena can be understood on the basis of geometric effects. The shape of (metal) nanoparticles is determined by the minimization of the particles free surface energy. According to Wulffs law, this requirement is met if (on condition of thermodynamic equilibrium) for all surfaces that delimit the (crystalline) particle, the ratio between their corresponding energies cr, and their distance to the particle center hi is constant [153]. In (non-model) catalysts, the particles real structure however is furthermore determined by the interaction with the support [154] and by the formation of defects for which Figure 14 shows an example. 

Considering chemisorption as chemical interaction, in our case interaction of oxygen with adsorption centers which are modeled by surface-adjacent superstoichiometric metal atoms we can write down... 

Structural information about the oxygenases provided limited insight into the mechanism (Schmidt et al. 2006). The crystallized enzyme from Synechocystis sp. PCC6803 is membrane associated and the interaction with the membrane is believed to be mediated by a nonpolar patch on the surface of the enzyme. This hydrophobic patch is thought to provide the necessary access of the protein to the membrane-bound carotenoids. Following withdrawal from the membrane, the substrate moves through the hydrophobic tunnel toward the metal center. The substrate orients the... 

These results suggest that the critical factor in the substrate-mediated intermolecular interactions which occur within the close-packed DHT layer is the inherent strong reactivity of the diphenolic moiety with the Pt surface. The interaction of adsorbates with each other through the mediation of the substrate is of fundamental importance in surface science. The theoretical treatment, however, involves complicated many-body potentials which are presently not well-understood (2.). It is instructive to view the present case of Pt-substrate-mediated DHT-DHT interactions in terms of mixed-valence metal complexes (2A) For example, in the binuclear mixed-valence complex, (NH3)5RU(11)-bpy-Ru(111) (NH 3)5 (where bpy is 4,4 -bipyridine), the two metal centers are still able to interact with each other via the delocalized electrons within the bpy ligand. The interaction between the Ru(II) and Ru(III) ions in this mixed-valence complex is therefore ligand-mediated. The Ru(II)-Ru(III) coupling can be written schematically as ... 

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