Cadmium clusters

Platinum-cadmium clusters, luminescent properties, 12, 773 Platinum carbenes... 

Cadmium clusters have been treated by Baetzold (47) using EH and CNDO calculations. With atomic valence electron configuration 4dl05s25p, the clusters are calculated to be weakly stable. Linear geometry is more stable than symmetric three-dimensional geometries or even the bulk crystal structure for small Cd clusters. Poor stability is a consequence of the closed atomic 5s shell in Cd. Unstable antisymmetric 5s molecular orbitals are filled in the small clusters, but the amount of bonding by 5p orbitals increases with size. This leads to the trend of increasing stability with size as observed in Table VIII. Compari-... 

CdS, PbS, CdSe, and ZnS clusters arc the semiconductor compounds studied most extensively in zeolites.[39,40] In addition, ternary systems such as ZnCdS have attracted the interest of many researchers.[41] An ordered array of cadmium clusters assembled in zeolite A was prepared in an attempt to produce heavy metal clusters with different distributions and gcometries.[42] (Fig. 8)... 

Fig. 8. Cadmium cluster (Cd9s+) in the sodalite cage of zeolite A. Ref. [43]...

Existing data on phytochelatins and related polypeptides show that they differ from MT not only in biosynthesis but also in structure. Whereas no 3D structure has yet been reported, electronic spectroscopy (c.d. and UV-Vis) and EXAFS data on Cd-7-EC peptides led to different proposals as to the nature of the cadmium binding in such peptides, polynuclear cadmium thiolate aggregates versus isolated Cd(SCys)4 units, respectively. However, contrary to the conclusion of the previous work, a recent X-ray absorption spectroscopy study on Cd-7-EC peptides and model systems provides evidence for the formation of a polynuclear cadmium cluster. " ... 

Lover T efa/1997 Electrospray mass spectrometry of thiophenolate-capped clusters of CdS, CdSe and ZnS and cadmium and zinc thiophenolate complexes observation of fragmentation and metal, chalcogenide and ligand exchange processes Inorg. Chem. 36 3711... 

The Model 412 PWR uses several control mechanisms. The first is the control cluster, consisting of a set of 25 hafnium metal rods coimected by a spider and inserted in the vacant spaces of 53 of the fuel assembhes (see Fig. 6). The clusters can be moved up and down, or released to shut down the reactor quickly. The rods are also used to (/) provide positive reactivity for the startup of the reactor from cold conditions, (2) make adjustments in power that fit the load demand on the system, (J) help shape the core power distribution to assure favorable fuel consumption and avoid hot spots on fuel cladding, and (4) compensate for the production and consumption of the strongly neutron-absorbing fission product xenon-135. Other PWRs use an alloy of cadmium, indium, and silver, all strong neutron absorbers, as control material. 

Swayambunathan V, Hayes D, Schmidt KH, Liao YX, Meisel D (1990) Thiol surface complexation on growing cadmium sulfide clusters. J Am Chem Soc 112 3831-3837... 

Metallothioneins (MT) are unique 7-kDa proteins containing 20 cysteine molecules bounded to seven zinc atoms, which form two clusters with bridging or terminal cysteine thiolates. A main function of MT is to serve as a source for the distribution of zinc in cells, and this function is connected with the MT redox activity, which is responsible for the regulation of binding and release of zinc. It has been shown that the release of zinc is stimulated by MT oxidation in the reaction with glutathione disulfide or other biological disulfides [334]. MT redox properties led to a suggestion that MT may possesses antioxidant activity. The mechanism of MT antioxidant activity is of a special interest in connection with the possible antioxidant effects of zinc. (Zinc can be substituted in MT by some other metals such as copper or cadmium, but Ca MT and Cu MT exhibit manly prooxidant activity.)... 

Cf produces two fission products that travel in opposite directions. If one projectile hits the sample, ions will be produced. These ions may then be focused and measured by TOF MS. The other projectile may be used to measure the start of the ionization process. This method has been used to study the ions produced from the ionization of metal complexes such as cadmium thiolates (33) and lanthanide phthalocyanine complexes (34). This method has also been used on metal oxides such as La203 to produce metal oxide cluster ions (35). 

L0ver, T. Bowmaker, G.A. Henderson, W. Cooney, R.P. ESl-MS of Some Cadmium Thiophenolate Complexes and of a Thiophenolate Capped CdS Cluster. Chem. Commun. 1996, 683-685. 

In order to check the results of the analysis, K-Nearest Neighbor distances were computed for the scaled data set Including the cadmium results. The median of the distances from a given laboratory to the three nearest neighbors ranged from 0.26 to 1.24 with the median distance between members of the cluster (1,2,3,5,6,7) equal to 0.79. The median distances of Laboratories 4 and 8 from members of this cluster were 1.24 and 1.22, respectively, supporting the view that these laboratories are outliers. 

Parhutik VP, Makushok IE, Kudriavtsev E, Sokol VA, Khodan AN (1987) An X-ray electronic study of the formation of anodic oxide films on aluminium in nitric acid. Electrochemistry (Elektrokhymia) 23 1538-1544 Kundu M, Khosravi AA, Kulkami SK (1997) Synthesis and study of organically capped ultra small clusters of cadmium sulphide. J Mater Sci 32 245-258... 

The role of 3Fe clusters is open to speculation. Some proteins appear to be functional only as the 3Fe form (e.g., AvFd and fumarate reductase). For others the 3Fe form may be an unfortunate side effect of having a reactive readily displaced ligand which is required for the enzyme mechanism as in aconitase. Because the 3Fe cluster can take up other metals (e.g., nickel, cadmium, or zinc) (Moura et al., 1986 Surerus et ai, 1987 Surerus, 1989), it is possible that the 3Fe form may be the precursor for... 

Zeolitic materials have been prominent amongst those so far studied by high resolution powder diffraction using synchrotron X-rays [36]. High definition synchrotron PXD data has been helpful in a number of framework structure determinations and has facilitated studies of planar faulting (see below). Successful Rietveld refinements of the framework structures of zeolite ZSM-11 [37, 38] and silica-ZSM-12 [39], and of the complete structures of zeolite Y containing cadmium sulfide [40] and cadmium selenide [41] clusters have been described. 

In aqueous solution, the mixture of solutions containing cadmium and sulfide ions induces a precipitation of CdS semiconductor. When adding a protecting polymer such as sodium hexainetaphosphate (HMP) in the solution, no precipitation is observed and a yellow solution remains optically clear, indicating the formation of CdS clusters. In reverse micelles, similar behavior of the latter is observed, as shown later. 

In the presence of an excess of sulfide ions, [Cd2+]/[S2 ] = 5, a strong change in the absorption spectra at low water content is observed compared to that obtained for a ratio of [Cd2+]/[S2-] equal to 2. By increasing the water content, the sharp peak disappears and a similar behavior as in the case of excess of cadmium is observed, i.e., a red shift in the absorption spectrum. The sharp peak observed at low water content increases with the relative amount of sulfide ions (45). This peak is attributed to sulfide clusters (55) formed on the CdS particles because of the high local concentration of sulfide ions. The disappearance of this peak when increasing the water content could be explained by the fact that sulfide clusters, with negative charges, are repelled to the center of the droplets and redissolve themselves inside the water pool. 

Controlled reduction of cadmium (or lead) ions on surfaces of nanosized silver (or gold) metallic particles results in the formation of double-layer colloids [532-534]. Depending on the coverage, the second layer can vary from being non-metallic clusters to quasi-metallic and metallic colloids. Growth of the second-layer particles can be monitored by absorption spectrophotometry. For... 

A higher level of size and morphology control in the incipient semiconductors has been accomplished in reversed micelles prepared from cadmium AOT [614] and from mixtures of cadmium AOT and sodium AOT [615] or, alternatively, by arresting particle growth by surface derivatization [592, 621, 622]. Indeed, surface derivatization of semiconductor clusters was first reported for particles in reversed micelles [621] the reversed micelles act to confine precursor ions and to control the growth of the semiconductor particles. Conditions are typically arranged so that, initially, there is no more than one metal ion (say Cd2+) per water pool. Addition of a heptane solution of bis(trimethylsilyl) selenium resulted in the formation of size-quantized metal selenide particles (say CdSe) in the reversed micelles. This solution could be evaporated to dryness and the resultant particles could be reconstituted in a hydrocarbon solvent Alternatively, addition of metal (say Cd2+) ions to the reversed-micelle-entrapped metal selenide particles, followed by the addition of alkyl(trimethylsilyl)selenium, RMSiMe3, led to the formation of alkyl-capped... 

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