FE MO method

The simplest semiempirical w-electron theory is the free-electron molecular-orbital (FE MO) method, developed about 1950. Here the interelectronic repulsions l/r,y are ignored, and the effect of the cr electrons is represented by a particle-in-a-box potential-energy function V" = 0 in a certain region, while V = oo outside this region. With the interelectronic repulsions omitted, in (16.1) becomes the sum of Hamiltonians for each electron hence (Section 6.2)... 

Although the simple FE MO method fares poorly for the conjugated polyenes, it works rather well for polymethine ions with the formula... 

Use the FE MO method to estimate the longest-wavelength electronic transition of... 

The FE MO, HMO, and PPP methods are restricted to planar conjugated molecules (e.g., butadiene, benzene, pyridine), and make the pi-electron approximation of treating only those valence electrons that are in pi MOs (those that have eigenvalue — 1 for reflection in the molecular plane) they assume the existence of a pi-electron Hamiltonian Hm of the form... 

Detn of Sn,Fe " Mo in titanium metal or its alloys by paper chromatographic-polarographic-colorimetric method) 50a)F.Cramer. "Paper Chromatography , Macmillan, London (1954)... 

LoJacono et al. (108) also utilized X-ray diffraction methods to study the structural and phase transformations which occurred in the Bi-Fe-Mo oxide system. They detected two ternary compounds containing bismuth, molybdenum, and iron. One of the compounds formed when the atomic ratio Bi/Fe/Mo = 1 1 1 the other formed when the atomic ratio Bi/Fe/Mo = 3 1 2. The X-ray data indicated a close structural relationship of the bismuth iron molybdate compounds with the scheelite structure of a-phase bismuth molybdate. Moreover, their structures were similar to compound X. The structure of the Bi/Fe/Mo = 3 1 2 compound was identical to the compound reported by Sleight and Jeitschko (107). The authors proposed that the structures of both of the compounds could be viewed as resulting from the substitution of Fe3+ in the a-phase lattice. In the Bi/Fe/Mo = 1 1 1 compound, 1 Mo6+ ion is replaced by 2 Fe3+ ions one Fe3+ ion occupies a Mo6+ site the other Fe3+ ion occupies one of the vacant bismuth sites. In the Bi/Fe/Mo = 3 1 2 compound, the Fe3+ ion replaces one Mo6+ ion while the additional Bi3+ ion occupies one of the vacant bismuth sites. 

Supported metallic Ni, Cr, Fe, Mo, Co, V, Ti, Sn, Ru, and Pd catalysts have been prepared with the help of the CVD method fundamentally using carbonyl and chloride precursors [16]. 

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

Various LCAO-MO Methods. In order to render tractable the problem of determining the molecular electronic eigenfunction, Fe, it is customary to assume the individual molecular orbitals to be functions of the atomic electron eigenfunctions, xr> centered on each atom. The molecular orbitals (MO s), it are taken to be linear combinations of the atomic orbitals (LCAO s), Xr-... 

The molar absorptivity of the pseudo-solution is 7.7-10" at 510 nm (sp. abs. 0.65). The method is of low selectivity. Numerous multivalent metals (e.g., Sb, Ge, Zr, Ga, Fe, Mo, and Ti) interfere. Small amounts of Ti, and Mo can be masked with hydrogen peroxide. Antimony, which often accompanies tin, can be masked with citric acid. 

New Fe-Mo-Ti mixed oxides prepared via the sol-gel method comparison of the textural properties with solids obtained by impregnation... 

The aim of this work is to develop new Fe-Mo containing mixed oxides highly dispersed in a titania matrix, prepared by the sol-gel method, and to compare these materials to those of iron molybdate prepared by conventional methods (i.e. impregnation). Here, we report the preparation of sol-gel derived iron molybdenum titanium mixed oxides. The bulk composition and the textural properties of these materials are investigated by elemental chemical analysis and N2 adsorption, respectively. 

The Mo—Fe protein in the native state exhibits an EPR spectrum due to two S = 3/2 centers54) which were shown to be identical to the signals observed for the Fe—Mo cofactor64) with features around g = 4.3,3.1 and 2.0 for the native enzyme. These M-centres contain about 40% of the total iron54 74) which were associated with the S = 3/2 centers, as judged by conjunction of EPR and Mossbauer methods. The Mossbauer spectrum of both the S = 3/2 species and the cofactor, were studied in detail by Huynh et al. 33) and the spectral features could be decomposed in 6 subcomponents suggesting the existance of 12 iron atoms in 2 cofactors (S = 3/2)... 

Nitrogenase is another big target of cluster synthesis. The X-ray elucidation of the active center of the Fe-Mo cofactor and P-cluster (5) has accelerated the efforts to find rational preparative methods of trinuclear or cubane-type clusters containing molybdenum (6-9). The raft cores in these cluster complexes are one of the general structural units also in solid-state compounds, and the mutual relationships are very important. A number of review articles are now available on the syntheses, structures, and other properties of metal chalcogenide cluster compounds (6, 7,10-24). 

The thiomolybdate(VI) anions [MoO S4 ] (n = 0-3) have been prepared by a number of methods and, with the exception of [MoOsS] ", act as versatile ligands to a wide variety of metal ions (see Table 1). In each of the compounds listed in this table, the [MoO S4- p ion acts as a bidentate ligand to the metal and the resultant structural versatility has been clearly demonstrated for copper(I) (Table 2). In addition, thiomolybdate(VI) anions are of interest since they have special relevance to aspects of bioinorganic chemistry. Thus, [MoS4] has been widely used in the synthesis of Fe—Mo—S clusters, examples of which serve as spectroscopic analogues for the iron-molybdenum cofactor of the nitrogenases (see Section 36.6.2), and Cu—Mo—S aggregates, which are relevant to the copper deficiency induced by molybdenum in ruminant animals. 

Since the EXAFS technique has become practical, it has become a standard method for probing the metal site structure in metalloproteins. The technique has been applied to virtually every metalloprotein that has been isolated containing Fe, Mo, V, Cu, Mn, Zn, Ni, Ca, and other metals. In this section, the usefulness of the method is illustrated by choosing three different biological systems where XAS has contributed to structural determination. Readers are referred to several excellent reviews for an overview of the biological applications of XAS. ... 

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