Clusters, metal with encapsulated atoms

Rhodium also forms an unusually large number of clusters containing encapsulated hetero atoms as, for example, the [Rhn(S)2(CO)32]3 species whose skeletal structure is shown in Fig. 16-15, and a number that contain carbon atoms. It also forms both smaller, for example, Rh CO), and larger, for example, Rh H CO) clusters that have no encapsulated atoms. The Rh12 species has a very novel structure in which two Rl octahedra are linked together to form an Rh6 octahedron between them. Finally, rhodium also forms many mixed metal clusters, especially with plati-... 

While they are not strictly redox-containing dendrimers. Crooks and Zhao have encapsulated platinum and other metallic nanoparticles inside PAMAM dendrimers. The catalytic properties of these materials have been examined using cyclic voltammetry, and it was found that a gold electrode, modified with large hydroxyl-terminated PAMAM dendrimers containing clusters of 60 platinum atoms, was readily able to catalyze O2 reduction [98]. Similar results have been reported for palladium clusters encapsulated in the same hydroxyl-terminated PAMAM dendrimers [99]. 

In conclusion, metal atom clusters such as Moe-based cluster units are promising light emitters for the preparation of luminescent silica nanoparticles, hi addition, a magnetic property can be added in a simple one-pot microemulsion process by the co-encapsulation of cluster units with y-Fe203 nanocrystals. Then, already luminescent and magnetic nanoparticles can also be rendered plasmonic by growing gold nanocrystals on their surface. Finally we showed that the silica matrix efficiently prevent plants or human cells from the toxicity of the clusters. 

Very few examples are known, apart from solid state structures, where the sulfide acts as a bridge to more than four metal atoms. Two Rh clusters [Rh17(S)2(CO)33]3 and [Rh,0S(CO)22]2 have been reported in the literature77,78 where the sulfide is found interstitially in the center of the metal cluster and has contacts to nine and eight Rh atoms, respectively. In the former example an almost linear S—Rh—S unit (with d(Rh—S) as short as 2.16 A) is encapsulated in an Rh16 cluster, with four Rh—S contacts at about 2.33 A and four more at about 2.8 A.77 Other related systems are, for example, the [M6S,7]4 ions (13 M = Nb, Ta) which have been recently prepared by Holm and co-workers.80 Here, among other types of sulfide coordination, a /vS has been found in the base of the bell-shaped ions. 

In the case of rhodium, however, it was demonstrated early that in the synthesis of [Rh6C(CO)l5]2 the encapsulated carbon atom originated as chloroform, which had reacted with the rhodium carbonyl anion [Rh7(CO)l6]3- (59). In the cobalt analog, [Co6C(CO)l5]2-, the carbon atom is derived indirectly from carbon tetrachloride [via Co3(CO)9CCl] (60) Both these syntheses are performed under mild conditions, and there are apparently no examples of carbidocarbonyl clusters of cobalt or rhodium prepared directly from the metal carbonyls under pyrolysis conditions. 

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