Cluster complexes, heterometallic.

In the second cluster, the two Ru6 octahedra are linked through two palladium atoms. The third cluster contains two additional palladium atoms. The Pd4 skeleton adopts the form of a bent square. The two Ru6 octahedra have local structures similar to those in the second cluster, but their relative orientation is now twisted. Apparently, formation of these heterometallic cluster complexes does not result from a simple combination reaction between cationic and anionic complexes but is accompanied by partial redox reactions.900... 

Braunstein, P. and Rose, J. (1998) Heterometallic clusters for heterogeneous catalysis, in Catalysis hy Di- and Polynuclear Metal Cluster Complexes (eds R.D. Adams and... 

Most heterometallic cluster species containing both lanthanide and transition metal elements in the cluster core structure will not be included. Such cluster complexes are of tremendous fundamental and practical interests, and interested readers would be better served with review articles dedicated just to this particular family of lanthanide-containing materials (Benelli and Gatteschi, 2002). However, heterometallic clusters containing recognizable cluster motifs composed solely of lanthanide elements will be discussed. 

It is convenient to divide this material according to whether the cluster complex is homo- or heterometallic in nature, although many of the principles apply to both cases. 

F.18 Synthesis of cluster compounds by photolysis of azido complexes [heterometallic Au clusters]... 

Cluster complexes may be isolated (extremely rare), connected via common ligands (more frequent), or connected (most frequent) by common edges, faces, or vertices (with steeply decreasing frequency) to assemble oligomers, chains, layers, or networks of clusters. The heterometallic clusters alone may be understood as polar intermetallics of (usually) low dimensionality. Together with halide ligands, they form metal-rich halides. Thus, these solids are excellent... 

A feature of transition metal cluster complexes is that they can undergo electron transfer reactions to give mixed-valence clusters. A second feature of these complexes is that, in addition to homometallic clusters, heterometallic cluster complexes can be prepared that have two or more different metals within the cluster core. Examples of such complexes for which emission has been observed are (DENC)3Cu 2Cu°Co(NS)2CU and (DENC)3Cu3M(NS)CU [DENC = iV,A -diethyl-nicotinamide NS = 5-methylhydrazine-carbodithioate Schiff base M = Co(II), Ni(II), Cu(n), Zn(n)]. For these complexes the emission maxima and lifetimes are shown in Table The emission from all the complexes is centered on the... 

The addition of OMe to cluster-coordinated GO has been used in the electrospray spectrometry of metal carbonyl complexes.Heterometallic clusters such as Gp Fe(GO)(/x-GO)2Ru2(GO)4(//-H) /x-MeG(GOO)Gl have been obtained upon carbonyl substitution with MeG(Gl)HGOOH on the tetra-heterometallic precursor. An efficient synthetic method for Ru3(GO)i2 starting from ruthenium dioxide hydrate has been reported in the presence of formic or acetic acid, carboxylate complexes are obtained. These favor the reductive carbonylation of nitrobenzene to aniline and A,iV -diphenylurea. 

Recently there has been considerable interest in the reactions of mixed-metal cluster complexes with oxide supports. To a large extent this emanates from the established phenomena within the field of heterogeneous catalysis which show that unusual activities and selectivities can be observed for supported "alloy catalysts [70]. The development of the solution chemistry of heterometallic cluster complexes has reached the stage of providing several series of related complexes which can be used as the basis of systematic studies. Indeed, the complexes Co2Rh2(CO)j 2 Co3Rh(CO)j 2 were reacted with silica and alumina some years ago with the aim of generating new alloy catalysts... 

Reactions of clusters with mononuclear or dinuclear metal complexes frequently provide a method of expanding the metal core nuclearity under controlled conditions. The majority of medium- and high-nuclearity homometallic clusters has been prepared from lower-nuclearity cluster precursors by thermolyses ("heat-it-and-hope ) reactions. This is less true of the heterometallic clusters in this... 

The novel T 2- X2-SiO bonding mode observed in these heterometallic complexes may have relevance to the stabilization of unsaturated, catalytically active heteronuclear systems. It also provides a new structural model for the bonding of small clusters or aggregates onto silica [1], a dominant theme in heterogenous catalysis. 

In addition to these homometallic (rhodium) clusters, several hetero-metallic clusters of the type [M M CO o]2, where M and M1 are each different metals selected from the Co, Rh, Ir triad (jc = 1-11), have been described and claimed to be useful catalysts in the reaction between carbon monoxide and hydrogen to produce oxygenated products (68, 69). These complexes can be prepared from the heterometallic dodecacar-bonyl complexes, [MuM (CO)12] (M, M1 = Co, Rh, or Ir y = 1-3), by simply mixing the appropriate dodecacarbonyl species in THF under nitrogen and then adding water (70). They can be isolated by adding a suitable cation e.g., Al3+, Mg2+, Ca2+, etc. 

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