Dimeric clusters

A more detailed representation of the reaction requires more intimate knowledge of the enolate structure. Studies of ketone enolates in solution indicate that both tetrameric and dimeric clusters can exist Tetrahydrofliran, a solvent in which many synthetic reactions are performed, favors tetrameric structures for the lithium enolate of isobutyr-ophenone, for example. ... 

The major product obtained from the reaction of TeCU with (McsSijsN is determined by the stoichiometry. When approximately equimolar amounts of the two reagents in THF are used the dimeric cluster TceNs (stabilized by coordination to four TeCU molecules) is obtained in high yields (Section 5.2.8). When the same reaction is carried out in acetonitrile with a molar ratio of 2 1, followed by treatment of the product with AsFs in SO2, [Tc4N2Cl8][AsF6]2 is obtained Section The dication [Tc4N2Cl8] in this salt is the dimer of the hypothetical tellurium(IV) imide [Cl3Te-N=TeCl]. ... 

R. 0. Holmes, R. R., unpublished work). The cube may be viewed as a condensation product of the dimeric cluster according to the expression in Equation 6. Hence, the dimeric cluster may serve as a precursor on the way to the cubic form. 

Since NMR studies suggest a Ca—Cf, double bond in 26 to be significantly weak, a better representation of the cuprate/enone complex is as a cupriocyclopropene 27, which is represented in the reaction shown in Figure 25. However, the indispensability of the dimeric cluster in the crucial C—C bond-forming step is not clearly understood. 

Nickel-iron hydrogenases [NiFe] (Figure 8.2) are present in several bacteria. Their structure is known [22, 23] to be a heterodimeric protein formed by four subunits, three of which are small [Fe] and one contains the bimetallic active center consisting of a dimeric cluster formed by a six coordinated Fe linked to a pentacoordinated Ni (III) through two cysteine-S and a third ligand whose nature changes with the oxidation state of the metals in the reduced state it is a hydride, H, whereas in the oxidized state it may be either an oxo, 0, or a sulfide,... 

Li2[Te(N Bu)3] 2 is an air- and moisture-sensitive solid that can be stored for several months in the drybox. This dimeric cluster adopts a distorted hexagonal... 

Figure 5.4. The highest occupied molecular orbital of a Si911,2 dimer cluster. The top two silicon atoms comprise the surface dimer, and the remaining seven Si atoms contain three subsurface layers which are hydrogen terminated to preserve the sp3 hybridization of the bulk diamond cubic lattice. The up atom is nucleophilic and the down atom is electrophilic.

Such higher order prerequisites could be fulfilled by ensemble operation of several sites. For example, a dimeric cluster of cuprous ions on silica gel is very active for the oxidation of CO with NzO at room temperature, but isolated cuprous ions are entirely inactive for this reaction 60). More interesting selectivity may be found in the reaction of olefins with methylene complexes the reaction of olefins with mononuclear methylene undergoes an olefin metathesis reaction, but the reaction of ethylene with bridging methylene in /i-CH2Co2(CO)2(Cp)2 61), /<-CH2Fe2(CO)8 (62), and /<-CH2-/i-ClTi(Cp)2Al(Me)2 (65) (Cp = cyclopentadiene) leads to propene formation (homologation reaction). 

Platinum cluster complexes with Pt—Pt bond(s) having various oxidation states are well known, and many exist in low-valent oxidation state, such as a series of [PtsCCOeln and phosphine or isocyanide clusters 1-9). A platinum ion with an odd d electron tends to form a dimeric complex having a Pt—Pt single bond involving the unpaired electrons. Monovalent platinum forms dimeric cluster complexes with a d -d configuration (10-14) and tervalent platinum forms d -d ... 

Dimeric Clusters. By far, the largest body of thermodynamic Information exists for vapor phase homonuclear dlatomlcs. Our source of data was the JANAF tables and supplements. This compilation Is by no means exhaustive but there are certainly sufficient X2 type molecules listed (20) to provide a suitable test of the model. Due to the prefactor (a c ) l In the configurational Integral (Eq. 1), an amount Rln2 was added to the... 

Let us consider a crystal, whose structural units are MV d —d dimeric clusters. The Hamiltonian of the crystal can be presented as ... 

Sihcon (100) surfaces play a decisive role in many technologically important device applications. The stiucture of the surface has been widely studied, both experimentally and theoretically [16-18]. The knowledge of the surface provides a good reference for the study of the interactions of the surface and the complex molecules. Thus, in this research, we investigate the issue of attachment of aromatic molecules to the dimerized sihcon (100) surface. This is an importance in device fabrication. In theoretical research, slab models and cluster models have been extensively used to describe Si(lOO) -2x1 surfaces [16-18]. Among these models, the cluster model has been extensively used in theoretical research of the surface since it is simple and amenable to model the fundamental features of the surface. The smallest cluster model for the 2x1-reconstmcted Si(lOO) surface is the one-dimer cluster, which includes two surface... 

Si atoms representing the dimer structure, four second layer silicon atoms, two third layer silicon atoms, and one fourth layer silicon atom. Although this cluster can be used to simulate the bulk feature of sihcon, the one dimer cluster does not describe the surface reaction adequately [17]. In order to adequately describe the surface at low computational cost, we adopt the three dimer cluster model S121H20. As the energy gain per dimer for the three-dimer cluster is between 0.15-0.20eV and in agreement with the slab results to... 

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