Molecular bimetallic cluster compounds

In view of the extensive literature covering the syntheses and structures of bimetallic metal carbonyl clusters, it is even more surprising that few attempts to use the fadle decomposition of these compounds in the preparation of bimetallic colloids have been reported. Although this would be an unnecessarily complicated route to colloids of misdble metals if the salts of these metals could be coreduced to the same end, there remains the possibility of preparing bimetallic partides of immisdble metals starting from well defined molecular bimetallic clusters of immisdble metals. Such dusters are known to exist desjnte the immis-dbility of their constituent metals in the bulk, and there is reason to believe that bulk immisdbility might not apply to very small partides due to the importance of surface effects. 

Supported bimetallic catalysts can be made by adsorption of a bimetallic precursor such as molecular cluster compounds, colloidal particles or dendrimer-stabilised particles. In several cases, homogeneous bimetallic particles have been found where the compositions lie within the miscibility gap of the bulk alloy (e.g. with PtAu particles). This suggests that when the particles are small enough and do not possess metallic properties, the normal rules do not apply. 

Bimetallic molecular cluster compounds containing gold will adsorb intact on supports, and the ligands may then be removed by heating, but only a few such compounds are available. Simple carbonyl complexes do not exist,... 

A variety of metal cluster compounds have been chemically bound on amorphous metal oxides and entrapped inside zeolite cages by new preparative tools such as surface organometallic chemistry and the so-called ship-in-bottle technique. They oflier much promise as molecular precursors for rational preparation of tailored metal catalysts having a uniform distribution of discrete metal-bimetallic ensembles, namely, organometallics which are active for catalytic reactions. They also provide advantages as metal precursors to achieve higher metal dispersions and well-managed metal... 

ABSTRACT. Recent studies of supported and unsupported naked metal clusters of low-nuclearity are examined with the aim of comparing their structure and reactivity to those of molecular clusters. It is shown that naked clusters can be prepared with a nuclearity comparable to that of molecular clusters. Moreover, their structure is flexible in response to adsorbates which act as the ligands in coordination compounds. Transformations of molecular clusters into naked clusters and vice versa are examined. The reactivities of unsupported clusters (cluster beams) and of low-nuclearity bimetallic clusters involving two complementary active sites are also discussed. 

Ugo R, Dossi C, Psaro R (1996) Molecular metal carbonyl clusters and volatile organometallic compounds for tailored mono and bimetallic heterogeneous catalysts. 1 Mol Catal A 107 13... 

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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