Cluster intermediates, molecular synthesis

Cluster Intermediates in the Molecular Synthesis of Solid-State Compounds... 

K. 17 Cluster intermediates in the molecular synthesis of solid-state compounds... 

The reactivity of species with open structures is certainly relatively much higher than that of the equivalent closed derivatives since open polyhedron faces make the interaction of other chemical agents with cluster HOMOs and LUMOs much more probable. That is directly related to the formation of Lewis acid-base mWo-carborane complexes described above. Furthermore the reactivity of open-cluster species is also enhanced by the presence of three-center B-H-B bonds which originate occupied and unoccupied molecular orbitals with relatively high and low energy respectively. This class of compounds is, in general, therefore an excellent intermediate for synthesis. 

A simplified series of reactions between a hafnium salt and sulfuric acid is given in Fig. 4.3. The reactions showcase important facets of thin-film synthesis (but do not address the precise identities of intermediates or complexities of aqueous hafnium chemistry.) In the first step, a hafnium oxide chloride crystal hydrate is dissolved in water to disperse small hafnium-hydroxo molecular clusters. Sulfato ligands are subsequently added in the form of sulfuric acid. Since sulfato binds more strongly than chloro, hafnium-hydroxo-sulfato aqueous species are created. Under mild heating, these species readily poly-... 

The existence of a transit pool of free iron , which would be in equilibrium with iron-containing proteins, is a thermodynamic necessity, but its size is probably extremely small in normal conditions. Microsomal membranes contain nonheme-iron which is released upon incubation with some intermediates of heme synthesis (reviewed in ref. [155]). The resulting free-iron pool does initiate lipid peroxidation in vitro. In the cytosol, the iron-transit pool would be composed of Fe(III) and/or Fe(II), complexed with low-molecular-weight chelators, possibly in the form of polynuclear clusters [149],... 

Metal vapor techniques provide unique means for cryochemical solid-phase synthesis of metal-containing systems. In this way, metastable compounds, whose existence earlier was only supposed, have been obtained [7]. Besides, cryochemical processes produce stabilized small metal clusters of quantum type, which are the intermediate form of matter between isolated atoms and bulk metal [8, 9]. However, known methods of cryochemical solid-phase synthesis used low-molecular-weight matrices, in which the initial products of such a synthesis can be conserved only at low temperatures, when the matrix is enough rigid to hinder transformation or loss of these products. 

The mass separation of the major cluster of peaks was foimd to be 108.25 Da as expected from the synthesis. The mass separation of 18 Da between peaks within a major cluster indicated the loss of H2O and tire formation of intramolecular closed loops. The data indicated also that the percentage of closed loops did not vary with oligomer size, and that the molecular structure was intermediate between branched-linear and a simple ladder structure, with no evidence that fully condensed structures had been formed in significant amounts. ... 

Elemental semiconductor clusters encaged in zeolites provide a valuable opportunity for gaining a fundamental understanding of semiconductor clusters because stoichiometry is not a concern in the synthesis. Selenium is of interest because it has an intermediate electrical conductivity and a negative coefficient of resistivity in the dark hence it is markedly photoconductive. It has uses in, for example, photoelectric devices and xerography. When Se is sorbed into a molecular sieve, it gives markedly different optical absorption spectra from those of the bulk material. 

At 220 °C and 50 atm CO, Ru3(CO)i2 is a catalyst in CH3CN for the conversion of 1 into 2 and 3 [9]. The selectivity in the synthesis of 2 was similar to the one observed with Fe(CO)s. As it is known that aromatic nitro compounds, and more easily nitroso compounds, react with Ru3(CO)i2 to give imido complexes in which the nitrogen atom is coordinated to all of the three ruthenium atoms of the cluster skeleton [10-12], the nitrene complex 4, possible intermediate in the reaction, has been synthesised (eq. 2) and its crystal and molecular structure determined [9] ... 

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