Condensation clusters

Fig. I. Experimental setup the clusters are emitted from the cluster condensation cell, passing as a particle beam through a differential pumping stage into the focus of a time-of-flight mass spectrometer, where they are ionized by a laser pulse.

The cluster condensation can be carried on the chains of octahedra sharing edges can be joined to double-strands and finally to layers of octahedra (Fig. 13.18). Every layer consists of metal atoms in two planes arranged in the same way as two adjacent layers of atoms in a closest-packing of spheres. This is simply a section from a metal structure. The X atoms occupy positions between the metal layers and act as insulating layers. Substances like ZrCl that have this structure have metallic properties in two dimensions. 

Alpha cluster condensation in threshold states of self-conjugate 4n nuclei... 

Of course, valence electron concentration is not only related to the metal atoms but also to the number and valence of the ligands. Ligand deficiency creates vacant coordination sites at metal atoms and results in cluster condensation, which is the fusion of clusters via short M-M contacts into larger units ranging from zero- to three-dimensional. The chemistry of metal-rich halides of rare earth metals comprises both principles, incorporation of interstitial atoms and cluster condensation, with a vast number of examples [22, 23]. 

Figure 4.28. Schemes of octahedral cluster condensation, (a) Vertex-sharing, (b) edge-sharing and (c) face-sharing. In these examples octahedra centred by interstitial atoms are shown.

The scheme of cluster condensation or cluster fragment condensation leads eventually to structures observed in bulk metals. Particularly through extensive condensation of tetrahedral and octahedral clusters, arrangements closely related to the hexagonal and cubic close-packed structures can be obtained. Condensation also of icosahedral five-fold symmetrical clusters may be related to crystalline and quasicrystalline metallic structures. 

Several diynyl complexes react with other metal substrates, the proximity of the a-bonded metal to a multimetal system often resulting in further cluster condensation. 

Photolysis of 1 and the J/MCM-41 complex provides evidence of cluster condensation in the pores of MCM-41. A darkening of the sample and a bathochromic maxima shift are observed for both samples. This parallels the solution chemistry of I whereby the photochemical reaction of leads to the nanocluster [Cu5o(TePh)2oTei7(PEtPh2) ]4 [6]. Although it is unlikely the same reaction path is followed in our (solid) studies, the UV data are consistent with the formation of higher nuclearity species. 

Figure 1 Linkage Tree. Analysis of nine population clusters, condensed from data obtained by studying 42 populations. The genetic distance 0.2 represents approximately 150,000 years. Source Figure 2.3.3 from Ref. 12.

In the panicle synthesis, metal atoms produced by the heating collide with the inert gas atoms to decrease the diffusion rate of the atoms from the source region. The collisions also cool the atoms to induce the formation of small clusters of fairly homogeneous size. The clusters grow mainly by cluster-cluster condensation to give nanopaiticles with a broader size distribution. A convective flow of the inen gas between the warm region near the vapour source and the cold surface carries the nanopanicles to the cooled finger, where they are let to deposit. The inen gas pressure, the evaporation rate, and the gas composition can control the characteristics... 

The structures of reduced oxoniobates frequently contain Nb-Nb bonded units which can be discussed in terms of Nb60i2 clusters condensed in one, two or three dimensions. Some representative compounds with such condensed NbeO cluster units are shown in Fig. 11. 

Fig. 2. Principle of cluster condensation for (a) M Xg-type clusters (as in GdjClj) and (b) MgXj -type clusters (as in NaMo40g or including interstitial C atoms in e.g. GdiljC).

In what follows, the existing metal-rich halides are discussed first along the line of their structural chemistry. As an ordering scheme, the increasing degree of cluster condensation is used whether the Z atoms are present or not, i.e. the kind of R/X framework alone is used as a guideline. The arguments used to understand the... 

The previous structures, which contain distinct R octahedral clusters, necessarily have R/Z > 6. When R/Z > 4, we can find a finite number of these clusters condensed to give larger molecular units. For rare earth halide systems, only edge-sharing octahedra have been observed, as delineated in sect. 2, in which only two octahedra are involved and the interstitial moiety is a C2 dimer. Satpathy and Andersen (1985) applied the LMTO-ASA method to produce the energy DOS illustrated in fig. 43. Their model examined the interaction between an isolated GdioCljs cluster with two... 

Exo-polyhedral interactions (Figure 5.19) do not affect the skeletal bonding in individual monomeric units and hence Wade s rales can stiU be applied. These macro-polyhedral boranes where Wade s rule is apphcable can be called connected polyhedral boranes, in contrast to condensed polyhedral boranes in which the monomeric units share one or more boron vertices and do not obey Wade s rale. In order to be applicable to condensed polyhedral boranes as well, Wade s rule can be extended by incorporating a new variable, m, corresponding to the number of polyhedra. In Wade s n-i-l-i-p rale, 1 is added to include the core BMO. If m closo clusters condense to form a condensed polyhedral borane, there will be m core BMOs. Thus, the n-El-Ep rale can be modified to where m is the... 

Electronically, all chlorides and bromides containing the isolated [Rs(C2)] cluster ( condensed clusters with hexadeltahedra are not known ) with the formula types [Rs(C2)]X9 and A[R5(C2)]Xio may be grasped... 

Keywords Aluminum Capping principle Closed-shell principle Clusters Condensed clusters Copper Electron-counting rules Gallium Gold Jellium model Nanoclusters Palladium Polyhedral skeletal electron pair theory Silver Tensor surface harmonic... 

Figure 5-21. Derivation of the appropriate number of electrons for M atoms in MgOc type clusters condensed via corners of the Mg octahedra. The M atoms are distinguished according to three different functionalities (see text).

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