Clusters geometries

Metal-promoted alkyne-insertion reactions afford another good method (see structure 12 for cluster geometry and numbering)... 

The influence of electron-count on cluster geometry has been very elegantly shown by a crystallographic study of the deep-red compound [K(ctypt)]g [Ge9]- [Ge9] .2.5en, prepared by the reaction of KGe with cryptand in ethylenediamine. [Ge9] has the C4, unicapped square-antiprismatic structure (10.10c) whereas [Ge9]- , with 2 less electrons, adopts a distorted Dit, structure which clearly derives from the tricapped trigonal prism (p. 153).The field is one of... 

Our optimized cluster geometries agree well with other reported results for most part. One noticeable exception, however, is the case of Niia for which we find a capped distorted trigonal anti-prism structure with a central atom to be the most stable geometry, while the previously proposed distorted icosahedral structure was found to be unstable. We note that no full geometry unrestricted Optimization was done in obtaining the structure of Ref. 13. 

The complexity of the particle size related changes in the cluster geometry and electronic structure renders the results of the theoretical calculations extremely useful when analyzing the experimentally observed trends. 

Harris KDM, Johnston RL, Habershon S (2004) Application of Evolutionary Computation in Structure Determination from Diffraction Data 110 55-94 Hartke B (2004) Application of Evolutionary Algorithms to Global Cluster Geometry Optimization 110 33-53... 

The (/x3-X)Co3(CO)9 core, which has three tetrahedral Co(CO)3 units each bonded to a central entity in a trigonal array, is a common cluster geometry, as are analogs with Co substitution. A recent example of such a structure is via the reaction of Co2(CO)8 with (C6F5)2S, which yields (M3-S)Co3(C6F5)(CO)8.82... 

Synthesis and characterization of an Al69 cluster which can be regarded as a slightly modified Al77 cluster show the extreme sensitivity of the cluster geometry— even with the same ligand—to reaction conditions and number of ligands. Many more clusters will have to be synthesized to get a consistent picture of their formation and, consequently, the mechanism of metal formation which represents, as already mentioned, one of the oldest chemical processes in history. 

Johnston, R.L., et al., Application of genetic algorithms in nanoscience Cluster geometry optimisation. Applications of Evolutionary Computing, Proceedings, Lecture Notes in Computer Science, Springer, Berlin, 2279, 92, 2002. 

Synthetic routes to metalloboranes are briefly summarized. Two specific aspects of the field are selected for more detailed comment (i) the occurrence of exopolyhedral cycloboronation of P-phenyl groups (ii) oxidative cluster closure reactions. These topics are illustrated by reference to reactions of closo-BioHio nido-B9H12 and arachno-BoHiU" with a variety of Ir1 complexes, and several novel metalloborane cluster geometries (as determined by X-ray diffraction analysis) are described, notably nido-TIr(BoHi )H (PPh3)2], i so-ni do-[ IrC(OH)B8H6(OMe) (CgH PPh )... 

The 4 1 structure appears to be foundation for other cluster geometries. These (Fig. 4.6) can be constructed by uniting 4 1 clusters via faces to give the 6 2 and 8 3 clusters, by edges to give a 7 2 cluster, or by corners to give an alternative 7 2 cluster and the 16 4 cluster. 

The forces uniting these clusters seem to be relatively weak, as the overall cluster geometry appears to vary both with temperature, composition, and oxygen partial pressure. Broadly speaking, relatively isolated 4 1 clusters are found at the highest temperatures and in iron-rich compositions. As the temperature and relative amount of iron falls, more complex clusters are found. To some extent it is as if the 4 1... 

As in the case of wiistite, one of the earliest applications of atomistic simulations was to explore the likely stability of this defect cluster. It was found that not only the 2 2 2 arrangement but also other cluster geometries were preferred over isolated point defects. 

Starting from a Li+ surrounded by 5 water molecules (all in the first solvation shell), we have started a DFT Molecular Dynamics simulation, with a time step of 0.5 femtoseconds. In Fig. 6 we report a plot of the system at four different times. To better visualize the evolution of the cluster geometry, we have drawn, in Fig. 6, a fictitious bond between the ion and the water oxygen, if the distance is below 2.535 A. 

Iron-centered tetradecker sandwiches, when in contact with oxygen on silica, undergo oxidative fusion with ejection of iron to generate 12-vertex Co2C4B8 clusters.83 The cluster geometry, however, depends on the nature of the substituent X at B(3) in the iron sandwich. When X = H or Cl, the isolated species are of type 62, also obtained directly from C0C2B3 complexes as described in Section 3.01.4.1 64 when X = Me, the cluster produced is 77.84... 

This field has been well supplied with review articles.473-476 A variety of cluster geometries is known,2 and the new structures that have been reported have all been discovered fortuitously. 

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