Clusters M

The electrons supplied by the ligands and the valence electrons of the n metal atoms of an M cluster are added to a total electron number g. The number of M-M bonds (polyhedron edges) then is ... 

This chapter will mainly use examples of coordination phenomena involving transition metals, but where necessary and useful examples may include the coordination behavior of main group metals. There may also be occasion to give examples involving nonmetal systems. The ions used as examples will be both positive and negative ions such as the simple bare metal ions M+ or M , cluster metal ions M and M , and other metal containing ions M E (where E can be another metal, element, or ligand). 

TABLE 2.5. Proteins Encoded in the Genomic Region Covering Part of the A/m-cluster of Streptomycetes bluensis ISP5564 (ATCC27420) (Accession Codes X78972, AF126354)... 

Here, L2 represents the chemical property space corresponding to the VCL, d(x, rf) represents an appropriate distance metric between the lead compound ry and the compound , p xf is the relative weight that can be attached to compound (if all compounds are of equal importance, then the weights p(xy) = for each i), and Mis typically much smaller than N. That is, this problem seeks a subset of M lead compounds ry in a descriptor space such that the average distance of a compound from its nearest lead compound is minimized. Alternatively, this problem can also be formulated as finding an optimal partition of the descriptor space co into M clusters Ay and assigning to each cluster a lead compound rj such that the following cost function is minimized ... 

Excitation of the coupled A2, Bi states results in the decay rate designated X3 which appears to be nearly independent of cluster size. A small increase in the value of x3 appears to occur for (S02)m clusters from the monomer (0.6 ps) to the dimer (0.9 ps), but remains constant at about 1 ps for larger cluster sizes. A likely interpretation of the observed decay process can be found in a detailed computational study [6] which reports that following the initial vertical excitation of the 1 B state, the excited state wave packet travels from the Bi state into the double wells that result from the crossing of the 1A2 and Bi states. The transition of the excited state population into the double wells of the A2 and B states is believed to lead to the decay observed in the pump-probe experiment because the potential energy well minima of both of these states are outside of Franck-Condon region for the absorption of the probe laser pulse. Therefore, ion signal is not observed once the transition has occurred. The primary discrepancy between the computational results of Ref. [6] and the... 

Tl [CuSCuJ,(D-Pen0)l2ClJ,nH20 S-bridging M"+ cluster with Cu S3 and CuuN2S2 chromophores 23... 

The C-C bond in organic chemistry makes possible the formation of chains and rings. However, a feature of d block chemistry is the formation of M clusters (n 3) in which each M atom is bonded to at least two others, as well as to other ligands. Clusters may be divided into two categories ... 

The 18-electron rule can be applied - with some adjustments - to the structures and stoichiometries of polynuclear carbonyl complexes. To illustrate the principles, let us go back to the simple case of Mn2(CO)10. We found that the Mn atom was one electron short of 18 and that formation of the Mn-Mn bond - giving each Mn atom a share in an extra electron - would make up the deficit. In the general case of an M cluster, we can say that N, the number of two-centre, electron-pair M-M bonds, is given by ... 

Figure 12 Isosurfaces at fixed value (10% of max. amplitude) of the square modulus of the highest occupied (HOMO) and lowest unoccupied (LUMO) Kohn-Sham orbitals for the Si m cluster in the Si02 matrix.

The multielectron reduction of alkylazides catalyzed by various [4-Fe]n and [Mo-Fe]m clusters has been achieved by c.p.e. in homogeneous systems and at modified glassy-carbon electrodes [168-169]. Dithionite reduction of alkyl-azide is catalyzed by [Fe4S4( SC6H4-4-n-C8H 7)4 2 [170] and MoFe3S4... 

M-clustering-induced collapse of short PEO chains because we know that polymer chains in bulk or in a very concentrated solution adopt a random coil conformation, as with the 0-temperature [70,71]. In addition, the solvent quality of water for PEO decreases as the solution temperature increases. In order to differentiate these two scenarios, the temperature dependence of (Rg)/(Rh) is plotted in Fig. 15 to reflect the chain density distribution. The fact that (Rg)/ R ) 1.1 at lower temperatures, instead of 1.5 (an expected value for linear coil chains), reflects its branching structure because short PEO chains have a length similar to the PNIPAM segments between two neighboring grafting points. The decrease of (Rg)/ Rh) from 1.0 to 0.5 clearly reveals a change of the chain conformation. 

Perera and Amar (1989) found more detailed support for the structural control of caging in classical dynamics calculations on a model of Br2 in large clusters of Ar and C02. The dissociation channel was found to become closed, as a function of cluster size, between 11 and 12 C02 molecules in the BrJ(C02)M clusters, correlating with the appearance of double-capped minimum energy structures. This correlation was found in the Br2 Ar clusters as well. Collisions between a vibrating diatomic molecule in a cluster and the solvent particles may cause V-T energy transfer and rapid evaporation of the cluster. 

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