Naked metal cluster

Cobalt, nickel and copper naked metal clusters and olefin chemisorption models. G. A. Ozin, Coord. Chem. Rev., 1979, 28, 117-146 (45). 

Cryophotochemical techniques have been developed that (i) allow a controlled synthetic approach to mini-metal clusters 112), Hi) have the potential for "tailor-making small, bimetallic clusters (mini-alloy surfaces) 114,116), Hi) permit the determination of relative extinction-coefficients for naked-metal clusters 149), and iv) allow naked-cluster, cryophotochemical experiments to be conducted in the range of just a few atoms or so 112,150,151). 

Examples of the application of the mentioned rules to a few naked metal clusters according to Mingos and Wales (1990) are reported in Table 4.4. For each species the valence electron (s and p) count is made both on the basis of the component valences by adding/subtracting one electron for each negative/positive charge, and on the basis of the geometry and the number of vertices. 

Rudolph RW, Wilson WL, Taylor RC (1981) Naked-metal clusters in solution. 4. Indications... 

Rudolph RWT, Young RC (1979) The nature of naked metal clusters in solution. In Tsutsui M (ed) Fundamental research in homogeneous catalysis, vol 3. Plenum, New York, pp 997-1005... 

Nine-metal arrays in conventional coordination clusters are the confacial bioctahedron and two M4 cubanes linked through a non-cluster metal atom among naked metal clusters the M9 polyhedron is the tricapped trigonal prism or the monocapped square antiprism, and in gold clusters the metal array is the centred cube, the centred crown, or a fragment of the centred icosahedron. 

Elemental metals typically possess a continuum of orbitals in a wide conduction band. Calculations for bare metal particles suggest that scores or hundreds of metal atoms are necessary before the d band dispersion approaches the bulk value. Group theoretical considerations suggest that naked metal clusters possessing millions of atoms are still significantly different from bulk metals.Since the d band disjjersion in large carbonyl clusters will be pinched from above and below by the carbonyl 2n (that is, n ) and 5er bands, resjjectively, clusters may possess even narrower bands than naked particles of the same nuclearity. With wide dispersion as the metallic propierty of... 

Other studies of CO loss from small molecules include the photolysis of OCS on Ag clusters, in which an odd-even dependence on the number of Ag atoms in the cluster was discovered. OCS desorbs non-dissociatively from even numbered clusters, but dissociates to CO and AgnS on odd numbered clusters. This alternation correlates with the ionization potentials of the naked metal clusters, and the photoreactivity pattern can be explained in terms of a charge-transfer mechanism. A numerically efficient algorithm has been developed in the theory of ladder-climbing and IR multiphoton dissociation, and has been applied to HCO. ... 

Studies on both supported small metal particles and naked metal clusters indicate that the TOF tends to zero as the number of atoms per particle tends to unity. This amounts to saying that, in the limit of the smallest particles, all systems show antipathetic structure sensitivity. We have used particles" as a general term. They may be crystallites, but as the number of atoms per particle decreases their organization departs in general from that of a macroscopic crystal. These small particles (<1000 atoms d = 2.5 nm) are called clusters in the literature on naked metal particles (347). However, organometallic chemists may reserve the term cluster to describe a structure of metal atoms at least partly terminated by various ligands. 

L. Naked metal clusters (gas phase, matrix isolated)... 

We next consider the effect of cluster size on the adiabatic IP and EA of a naked metallic cluster. From Equation (10a), IP and EA for a spherical metallic cluster (u nm) are related to those for the planar bulk metal a oo) in the same medium by... 

Enormous developments in the area of soluble noble metal clusters protected with monolayers are discussed. Mass spectrometry has been the principal tool with which cluster growth has been examined. The composition and chemistry of clusters have been examined extensively by mass spectrometry. Besides gold, silver, platinum, copper and iron clusters have been examined. Clusters have also been examined by tandem mass spectrometry and the importance of ligands in understanding closed shell electronic structure is understood from such studies. Protein protected noble metal clusters belong to a new group in this family of materials. Naked metal clusters bearing the same core composition as that of monolayer protected clusters is another class in this area, which have been discovered by laser desorption ionization from protein templates. 

In the previous section we discussed gas phase metal dusters. We called these units of matter aked or elemental metd clusters in order to emphasize that they are most often composed of atoms of a single element and are not stabilized and surrounded by ligand molecules or fragments. Here, we discuss the electronic characteristics of ligated dusters, where a metal core is stabilized by an outer shell of ligands. These clusters possess chemical and physical properties completely different from those of the naked clusters and are sometimes referred to as molecular or organometallic dusters. Of course, there is no definition without exceptions, and examples of gas phase ligated metal clusters or of solid state naked metal clusters are also known. 

The schematic representation of the interaction of a naked metal cluster with its ligand shell allows one to analyze in detail the electronic interaction between the two fragments in terms of a) the relative positions of the metal and the ligand... 

Apart from the low-valent carbonyl clusters, there are also a number of middle- and high-oxidation-state clusters, such as (RO)jMo=Mo(OR)3 and CUResReCl " (13.1), which contain metal-metal multiple bonds.The halide cluster Mo6Clg" (13.2) contains an octahedron of molybdenum atoms with eight chloride ions bridging each of the faces. There are also a number of naked metal clusters of the posttransition elements, such as Sn. ... 

---