Mixed-metal clusters, molecular

Synthesis, molecular dynamics and reactivity of mixed-metal clusters. G. L. Geoffrey, Acc. Chem. Res., 1980,13,469-476 (29). 

Methyltin Halides and Their Molecular Complexes, 14, 63 Mixed-Metal Clusters, 18, 207... 

CP dynamics has also been very useful technique for estimation of the connectivities in the porous solids. Classic example in this case would be a clear distinction between Q2, Q3 and Q4 silicate sites in the molecular sieves on the basis of not only the chemical shift but also Tcp times which, as a result of no protons connected directly are much longer for Q4 sites (Si(OSi)4). Introduction of guest species in the pores has a dramatic effect on the CP-dynamics of the different silica sites. Thus, in the MCM-41 impregnated with the mixed metal clusters/counter-cation species, presence of embedded organic counter-cation lead to a significant reduction of Tcp and Tiph due to the presence of a different source of protons at the porous silica surface.21... 

Clusters and alloys are molecular species that may show different catalytic activity, selectivity and stability than bulk metals and alloys. Small metal clusters and alloy clusters have been studied reeendy for potential use as catalysts, ceramic precursors, and as thin films. Several fundamental questions regarding such clusters are apparent. How many atoms are needed before metallic properties are observed How are steric and electronic properties related to the number, type and structure of such clusters Do mixed metal clusters behave like bulk alloy phases ... 

Molecular Dynamics of H FeR CCO)-] and Related Mixed-Metal Clusters. Metal clusters have been shown to undergo a wide variety of fluxional processes in which carbonyls, hydrides, and even the metals themselves undergo rearrangement (25). Mixed-metal clusters are ideally suited for studies of fluxional processes because of the low symmetry which is inherent within their metal framework. In such clusters, the majority of... 

In addition to practical applications, metal cluster-derived catalysts, particularly intrazeolite metal cluster compounds, may aid in the identification of catalytically important bonding and structural patterns and thereby further our molecular understanding of surface science and heterogeneous catalysis. The ship-in-bottle technique for the synthesis of bulky metal-mixed metal cluster compounds inside zeolites and/or interlayered minerals has gained growing attention for the purpose of obtaining catalytic precursors surrounded by the interior constraint, imposing molecular shape selectivity. Such approaches may pave the way to offer the molecular architecture of hybrid (multifunctional) tailored catalysts to achieve the desired selectivity and stability for industrial processes. 

For metal clusters, it is now possible, through first principle theoretical (calculational) approaches, to predict and better understand vibrational spectra, optical band gaps, polarizability, quantum confinement, and stmctural predictions. One modern approach is to use pseudopotential density functional methods (PDFM), in particular to predict optical and dielectric properties. Similarly, using molecular dynamics simulations, it is possible to create models for cluster structures. This has been especially valuable for predicting a three-dimensional image for mixed metal clusters. Figure 6 illustrates computed stmctures for Cu-Ru bimetallic clusters. Note that in this case the dynamics simuiation predicted an enrichment of Cu at the edges and corners of the polyhedral structure. Indeed, this prediction was supported by later experimental catalysis data. 

This section is dedicated to a description of the chemistries of trinithenium and triosmium clusters that do not contain hydrocarbon ligands. This section should be viewed as an addition to the chemistry described in sections 32.5 and 33 of COMC (1982) and section 12 of COMC (1995) as most of the main themes have been developed in the previous two decades. Overall, the interest in the cluster chemistry of ruthenium and osmium during the period 1994-2004 has tended to focus mainly on higher nuclearity and mixed metal clusters in order to enhance the developments in catalysis and bridge the gap between molecular clusters and nanoparricles. However, triruthenium and triosmium clusters continue to play a pivotal role in the chemistry of ruthenium and osmium. Both classes of clusters can be, and are, used extensively as precursors for the synthesis of higher nuclearity clusters as well as the formation of mono- and bimetallic complexes. No up-to-date review of the chemistry of either Ru3(CO)i2 or Os3(CO)i2 and their compounds is available, but several annual reviews of the chemistry of mthenium and osmium, which include the chemistry of the trinuclear clusters, are available. ... 

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