Mixed-metal clusters pyrolysis

Examination of the methods that have been used in preparing the mixed-metal clusters listed in Table I reveals that the majority have been synthesized via four general types of reaction (1) pyrolysis, (2) addition... 

The pyrolysis of clusters in the presence of monomers, dimers, or other clusters usually requires much more severe reaction conditions than those previously discussed. Common starting materials such as Ru3(CO)12 and Os3(CO)i2 are themselves quite stable compounds. The reaction of Ru3(CO)I2 with a variety of compounds has yielded many mixed-metal clusters, as illustrated by Eqs. (13) (101, 161), (14) (96), (15) (30), (16) (28), (17) (28, 30), and (18) (30). 

The reaction of a carbonylmetalate with a neutral metal carbonyl has been labeled a redox condensation by Chini et al. (40, 41) and has been as widely used as a pyrolysis reaction for synthesizing mixed-metal clusters. Carbonylmetalates usually react rapidly with most neutral carbonyls, even under very mild conditions. A large number of mixed-metal hydride clusters have been formed via this type of reaction, primarily because the initial products are anionic clusters that in many cases may be protonated to yield the neutral hydride derivative. 

The 50% yield of H2FeRu3(CO)13 from Eq. (33) constitutes a significant improvement over previous pyrolysis methods (101, 161). These particular reactions can be scaled up, to produce several grams of the clusters in a single reaction, and consequently these mixed-metal clusters are readily available for reactivity studies. Clusters that contain three differ-... 

Pyrolysis of two or more metal complexes, usually carbonyls, can produce fragments that combine to form mixed-metal clusters. However, these reactions are usually not selective and often give only low yields. Any nonreaetive solvent having an appropriate boiling point may be used. The temperature should be high enough to cause ligand dissociation. 

One can imagine that the Pt2Ru4(CO)ig cluster compound is the intermediate in the reaction (2). The reaction can be further made via chemical decomposition of the compound to generate the bimetallic nanocatalyst. Indeed, Nuzzo et al. demonstrated that mixed Pt-Ru nanoparticles, with an extremely narrow size distribution (particle size 1.4 ran), were obtained. The Pt-Pt, Pt-Ru, and Ru-Ru coordination distances in the precursor (2.66, 2.64, and 2.84 A) changed to 2.73, 2.70, and 2.66 A, respectively, on the mixed-metal nanoparticles supported onto carbon black, with an enhanced crystalline disorder, as revealed by X-ray absorption fine stmcture (XAFS) spectroscopy. However, this example, using a controlled pyrolysis onto a designed molecirlar cluster, succeeds... 

Metal carbonyl clusters containing four or more metal atoms are made by a variety of methods osmium in particular forms a range of binary compounds and pyrolysis of Os3(CO)i2 yields a mix of products (equation 23.15) which can be separated by chromatography. 

Laser pyrolysis This is based on the heating with a laser beam of an organometallic reactantvapor (e.g., a metal carbonyl), mixed with an inert gas. The reactant vapors rapidly decompose to the atoms, which form clusters upon collision with inert gas molecules [29]. Nanoparticles of iron and iron carbides have been prepared in this way. 

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