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CHAPTER 9 Biosynthesis of the M-Cluster of Mo-Nitrogenase
No full textThe nitrogenase complex is responsible for the reduction of an inert gas, dinitrogen (N2), to a bioavailable form of nitrogen, ammonia (NH3). At the heart of the catalytic component of molybdenum (Mo) nitrogenase resides the iron-molybdenum (FeMo) cofactor (also termed the M-cluster). This chapter will describe the key proteins involved in the biosynthesis of the M-cluster and how simple [Fe4S4] clusters are transformed into a complex, [MoFe7S9C-homocitrate] M-cluster and subsequently transferred to the active site of nitrogenase
Synthesis and structure of [M(CO)4{(PPh2)2CHAu(PPh3)}] (M = Cr, Mo, W)
No full textThe reaction of diethyl ether solutions of Li[M(CO)4{(PPh2)2CH}] with [AuCl(PPh3)] gives [M(CO)4{(PPh2)2CHAu(PPh3)}] (M = Cr, Mo, W). The structure of the derivative with M = Mo was determined by single-crystal X-ray diffraction at 173 K. Crystals are monoclinic, space group P22, a = 13.552(3), b = 17.390(4), c = 17.390(4) A ̊, β = 90.94(2)°, Z = 4 and R(F) = 0.031. The two independent molecules are very similar. The molybdenum and the gold atoms display octahedral and linear geometries, respectively; the shortest intramolecular molybdenum-gold interaction is 4.52 Å. © 1995
Studies on Bis(imido) molybdenum complexes containing unsaturated hydrocarbon ligands
No full textThis thesis describes the synthesis and characterisation of molybdenum bis(imido) complexes containing unsaturated hydrocarbon ligands. A principal objective of the work was to examine the effect of various imido substituents on the coordination number of the complex and the orientations adopted by olefin and acetylene ligands. Chapter One highlights areas of transition metal chemistry relevant to the thesis, with particular emphasis on the psuedo-isolobal analogy between cyclopentadienyl and imido ligands, A convenient one-pot synthesis of molybdenum bis(imido) complexes of the type Mo(NR)(NR')Cl(_2).DME (R=R'=l-adamantyl, 2-t- BUC(_6)H(_4); R=2,6-i-Pr(_2)C(_6)H(_3), R'=t-Bu) is described in Chapter Two. Mo(N-l- adamantyl)(O)Cl(_2).DME has been synthesised, and its structure determined by single crystal X-ray diffraction.- The preparation of olefin complexes Mo(NR)(NR')(C(_2)H(_4))(PMe(_3))n (R=R'=l-adamantyl, n=l; R=R'=2-t-BuC(_6)H(_4), n=2; R=2,6-i-Pr(_2)C(_6)H(_3), R'=t- Bu, n=l) is outlined in Chapter Three. Structural information derived from NMR data has allowed comparison with metallocene-like olefin adducts. Chapter Four describes the synthesis of complexes containing σ-bound phenyl ligands (Mo(NR)(NR')(σ-C(_6)H(_5))(PMe(_3)) (R=R'=l-adamantyl, 2-t-BuC(_6)H(_4); R=2,6-i-Pr(_2)C(_6)H(_3), R'=t-Bu)) as potential precursors to benzyne complexes. Chapter Five describes the preparation of diphenylacetylene complexes Mo(NR)(NR')(PhC=CPh)(PMe(_3)), structural information derived from NMR data allows comparison with previously known metallocene-like acetylene complexes. Full experimental details for Chapters Two to Five are given in Chapter Six
Upper (a) and lower (b) right toothrow of <i>M</i>. <i>namaquensis</i> (MNHN-ZM-MO-1990-323).
No full textUpper (a) and lower (b) right toothrow of M. namaquensis (MNHN-ZM-MO-1990-323).</p
Interlayer composition and interface stability in Mo/Si multilayers studied with high-resolution RBS
No full textHeidemann B, Tappe T, Schmiedeskamp B, Heinzmann U. Interlayer composition and interface stability in Mo/Si multilayers studied with high-resolution RBS. Applied Surface Science. 1994;78(2):133-140
Synthesis of Bimetallic Phosphido-Bridged Isocyanide M−Mo (M = Mo, W) Complexes
No full textThe reaction of (M = Mo, W) with phosphine imide was
regiospecific with the isocaynide ligand regiospecifically coordinated to the Mo atom to
produce bimetallic isocyanide complexes (M = Mo, W; R
= Pr, CH2Ph, iPr). A single-crystal study of was
performed
a critical review of the phenomenon of bond-stretch and distortional isomerism in oxo and sulphido complexes of transition metals
No full textThis thesis describes studies directed towards the preparation of oxo compounds of the early transition metals with a view to assessing their potentials for exhibiting distortional and bond-stretch isomerism. Analogous sulphido complexes in the case of the M(E)X(_3)(PMe(_3))(_3) system (M= Nb, Ta; X= CI; E= S) have also been investigated in detail to provide a contrast with another chalcogenide element and further aid an understanding of the phenomenon of bond-stretch isomerism. Chapter 1 reviews the body of evidence to date on the phenomena of distortional and bond-stretch isomerism, and considers possible theoretical origins for the phenomena. Chapter 2 describes the detailed study of distortional isomerism in the six coordinate series of complexes Mo(O)X(_2)(PMe(_2)Ph)(_3) (X= CI, Br, I) and confirms the existence of two pure blue forms for the chloro and bromo cases. Chapter 3 assesses the evidence for further examples of distortional isomerism in the complexes W(O)Cl(_2)(PMe(_2)Ph)(_3), Mo(O)(NCS)(_2)(PMe(_2)Ph)(_3) and Mo(O)Cl(_2)(Pet(_2)Ph)(_3). Structural characterisation by X-ray crystallography has indicated the existence of a link between the orientation of the aikyl and aryl substituents on the phosphine ligands and the general features observed in their infrared spectra. Chapters 4 and 5 describe the seven coordinate oxo and sulphido-halide derivatives of niobium and tantalum which exhibit the phenomenon of bond-stretch isomerism. Compounds studied include M(E)X(_3)(PMe(_3))(_3) (M= Nb, E= O, S, X=C1, Br; M= Ta, E= S, X=Cl). The structures of these compounds have been re-investigated by X-ray crystallography in order to assess the significance of the co-crystallised isostructural NbCl(_4)(PMe(_3))(_3) contaminant. Chapter 6 summaries the evidence for and against distortional and bond-stretch isomerism. Chapter 7 gives experimental details for chapters 2-5
Electrical, morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells
No full textMolybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in ‘‘substrate configuration’’ thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films
Comportamento eletroquimico e caracterização microestrutural dos aços sinterizados e nitretados por plasma contendo MO e Ni
No full textDissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas.A fabricação de produtos via metalurgia do pó (M/P) é amplamente empregada na indústria, porém em aços sinterizados a presença de poros residuais decorrentes do processso de fabricação afeta o seu desempenho face à corrosão eletroquímica. Aplicou-se um tratamento superficial nas ligas, nitretação por plasma, visando melhorar a resistência à corrosão. Neste trabalho foram produzidas ligas na forma binária por M/P, Fe-5% Mo e Fe-10% Ni as quais foram sinterizadas a uma temperatura de 1250°C durante 2h e posteriormente nitretadas por plasma a uma temperatura de 540°C em uma mistura de 75%N2/25%H2 por 2h. O objetivo deste trabalho é avaliar o comportamento destas ligas sinterizadas, sinterizadas/nitretadas, frente à corrosão. Os ensaios eletroquímicos empregados para avaliar o comportamento das mesmas foram: Ecorr vs tempo, potenciodinâmico, potenciostático, realizados em uma solução de KNO3 1,25M, de onde derivaram os valores para os cálculos da taxa de corrosão. A Microestrutura das ligas sinterizadas e camada nitretada, foram analisadas por Microscopia Eletrônica de Varredura (MEV) e análise de energia dispersíva (EDAX). Entre as amostras de Fe-10%Ni sinterizadas e sinterizadas/nitretadas, não ocorreu diferença significativa nos ensaios potenciodinâmicos. O ensaio potenciostático revelou uma densa camada de óxido formada na liga sinterizada Fe-5%Mo, indicando a sua passivação. Em ambos os casos as amostras nitretadas não exibem uma melhora na resistência à corrosão
Mo-Doped Metal–Organic Frameworks for Efficient Nitrogen Reduction Reaction: A Density Functional Theory Study
No full textThe
activation of nitrogen molecules is one of the main obstacles
to electrocatalytic nitrogen reduction reaction (eNRR), which is closely
related to the d–p degree of coupling between d-orbitals of
metal active sites and p-orbitals of nitrogen. Herein, two types of
MOFsM2(DOBDC) and M2Cl2(BBTA)
(M = V, Cr, Mn, Fe, Co, and Ni)were systematically studied
via density functional theory (DFT) calculations. In addition, modification
strategies including Mo doping and coordination environment optimization
were successfully implemented. These modified MOFs can not only effectively
activate nitrogen but also maintain smooth ammonia desorption in the
NRR process. Especially, Mo(II)-Fe2(DOAnBDC) and Mo(II)-Fe2F2(BBTA) were considered potential eNRR electrocatalysts,
because of their high eNRR activity (UL = −0.60 V and −0.73 V, respectively) and selectivity.
Furthermore, the detailed electronic structural analysis revealed
that the increased eNRR activity is dependent on the unique d-orbitals
arrangement of Mo itself. Moreover, the charge transfer between the
−Fe–X–Mo– chains (X is a nonmetal anion)
regulated the Mo-d orbitals to enhance the d-p coupling, contributing
to the enhanced eNRR performance. These findings are of great significance
to stimulate the enthusiasm for studying ligand effects to find high-performance
eNRR catalysts
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