Cluster Chemistry

Abstract

whose fine structural details were not resolved until much later because of 1 2 exploded in the sixties and seventies through the efforts of many and especially those of the research groups of Chini, Lewis and Johnson; and Dahl. Size of these carbonyl clusters now has the impressive range of from to thirty~eight, the latter probably a number that has been exceeded or will soon be exceeded by the time this article is in print. A representative list of carbonyl clusters is given in Table II I see the most funda~ental differences between clusters and surfaces in the context of the coordination features of the peripheral urface) metal atoms [8]. The metal-metal coordination number of the peripheral metal atoms in molecular clusters ranges from two in 3-atom clusters to four in octahedral clusters to six in Pt3a(C0)~~2~ whereas the coordination number for flat metal surfaces is typically in the range of nine to six although it is as low as four for the (100) face of a body-centered cubic metal structure [8]. Metal~ligand coordination numbers for peripheral metal atoms in clusters are typically much larger than for the surface atoms in metals on which chemisorbed molecules or molecular fragments are presentThe metal-ligand coordination numbers are four in Os3(C0)12, three in sharp contrast to the surface metal-ligand coordination numbers which generally are less than one. Obviously, the disparity in values for these two types of coordination numbers decreases as molecular cluster size increases and metal particle size decreases and the crude analogy should be more useful for the large cluster-small metal particle comparisons. The features of the largest structurally established [14] molecular cluster~ Pt 38 (C0)~~2 -, nicely illustrate this point since this cluster has cubooctahedral form with exposed faces of (111) and (100) or ethyl, the nuclearity 1 n, is three and with R isopropyl, the nuclearity is two. All essentially have 16--electron square metal coordination sites. The d:Lmer consists of an essentially set of rhodium, hydrogen and phosphorus atoms (Figure 3). An edge~bridged set of three square planar Rh coordination spheres is :fotmd in the trimer as show"TI in Figure 4 for the crystallographically established {HRh [P (OG1 3 ) 3 ]z h complex.The chemistry of these rhodium hydrides is rather surprising. polynuclear hydrides to form not mononuclear H 3 Rh[P(OR) 3 ] 2 complexes but polynuclear rhodium polyhydrides~ equations (3) and (4).Nuclear magnetic resonance studies of these polynuclear polyhydrides have established for the dimer the tris(hydrido) bridged dimer structure illustrated in Figure 5.Both the trimeric and dimeric rhodium hydrides are very active olefin hydrogenation catalysts. Turnover rates at 20°C are between 1 and 100 per second. Reaction of the complexes with olefins is slow and complex whereas the reaction with hydrogen as noted above is virtually instantaneous.Hence the polyhydride is the first key intermediate in the catalytic cycle fluxional structure, and a key intermediate form im...

Structure and chemistry of a metal cluster with a four-coordinate carbide carbon atom

“…In further exploring the analogy between metal surfaces and metal clusters (2), we have attempted to demonstrate similar high reactivity for a carbide carbon atom in a molecular metal carbide cluster. We anticipated two features to be critical to such high reactivity in a cluster: a low coordination number for the carbide carbon atom and coordination unsaturation for the molecular cluster (3,4). These features have been realized (5,6) The publication costs ofthis article were defrayed in part by page charge payment.…”

“…This is a definitive demonstration of high reactivity for a carbide carbon atom under mild conditions in a molecular cluster. Thus, the necessary conditions, as set out by us earlier (3,4), of a coordinately unsaturated cluster with a low-coordinate carbide carbon atom have been realized in the putative …”

[μ-3-(8-Quinolyloxy)propanediyl]bis[dicarbonyl(η5-methoxycarbonylcyclopentadienyl)molybdenum(III)]

“…For general background to dimolybdenum alkyne complexes, see: Conole et al (1989Conole et al ( , 1990; Adams et al (1995Adams et al ( , 1996; Muetterties (1980); Gibson et al (1991); Brady & Pettit (1980); Sappa et al (1983Sappa et al ( , 1985; Raithby & Rosales (1985). For semibridging CO ligands, see: ; Klingler et al (1978).…”

“…Financial support from the National Natural Science Foundation of China (No. 20572064) The dimolybdenum alkyne complexes have been extensively examined (Conole et al, 1989(Conole et al, , 1990Adams et al, 1995Adams et al, , 1996 due to their potential applications in catalysis and materials (Muetterties, 1980;Gibson et al, 1991;Brady & Pettit, 1980). Moreover, such complexes can be used as precursors for constructing higher-nuclearity alkyne clusters (Sappa et al, 1983(Sappa et al, , 1985Raithby & Rosales, 1985).…”

Stabilization of Niobium(0) and Tantalum(0) in Mixed Metal Clusters containing Silver Atoms

“…Nb-C2-0 2 169.4(3); 2b: Ag-Ta 2.8884 (2), Ag-Ag' 2.8418(8), Ta-Cl 2.049 (4). Ta-C2 2.082 (5), Ag-Cl 2.784(4), Ag-C2 2.614 (5), Ag-Ta-Ag' 58.93 (2). Ta-Cl-01 177.6(4), Ta-C2-02 172.1 (4).…”