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Diffuse reflection spectroscopy is used to study color reactions of tungsten and molybdenum with pyrocatechol violet (PV) and phenylfluorone (PF) on a solid phase of polyacrylonitrile fiber impregnated with AN-31 (PANV-AN-31) or AV-17 (PANV-AV-17) anion exchangers. The relations of the analytical signals of complexes to sorption conditions in the batch mode, such as the acidity of solutions, presence of masking substances, and metal concentration, were found. A system was selected for the sorption-spectroscopy determination of 0.02-0.12 µg/mL of molybdenum in the presence of a fivefold excess of tungsten by sorption on PANV-AV-17 from a boric acid solution with pH 5 and reaction with PF. The sorption on PANV-AN-321 from boric acid solutions with pH 3 made possible the determination of the total concentration (0.8-4.2) x [10.sup.-6] M of molybdenum and tungsten by the reaction with PV. Keywords: diffuse reflection spectroscopy, molybdenum, tungsten, pyrocatechol violet, phenylfluorone, fiber impregnated with AV-17 and AN-31 anion exchangers DOI: 10.1134/S1061934813120101, Molybdenum and tungsten are relatively rare chemical elements that acquired great importance in contemporary technology. Both metals are strategically important and necessary for fulfilling the needs of state defense, in [...]

Molybdenum (Mo) isotope fractionation has recently been introduced as a new proxy in oceanography and biogeochemistry. It is therefore fundamental to understand the processes controlling Mo partitioning into modern marine environments. This study identifies the availability of dissolved sulfide as the dominant control on overall Mo removal from the water column in euxinic systems. Mo isotopic composition of surface sediments from different localities of the Black Sea demonstrates complete fixation of Mo only below 400 m water depth, above a critical concentration of 11 [micro]mol [l.sup.-1] aqueous hydrogen sulfide in the bottom water. The Mo isotopic composition of these sediments reflects the homogeneous seawater isotopic composition of 2.3 [per thousand]. In contrast, significant Mo isotope fractionation into less euxinic sediments is evident at shallower depths in the Black Sea, as well as in temporarily euxinic deeps of the Baltic Sea, consistent with the observed lower maximum sulfide concentrations in the respective water columns. Therefore, Mo isotope signatures in the modern Black Sea constrain the processes responsible for global Mo removal from the ocean by euxinic sediments. Furthermore, models of past ocean anoxia reconstruction have to consider that the seawater Mo isotopic composition is not per se archived in euxinic sediments. Keywords: molybdenum isotopes, Black Sea, heavy stable isotopes, isotope fractionation, sulfidity.

Relatively brief periods of severe paleoenvironmental change during the Jurassic and Cretaceous were associated with the widespread accumulation of organic-rich marine deposits, termed oceanic anoxic events (OAEs). These intervals involved abrupt global warming of ~5-10 [degrees]C, higher rates of continental weathering, elevated extinction rates, and large-scale perturbations to the global carbon cycle. The major OAEs also overlapped temporally the emplacement of large igneous provinces. However, despite being known as OAEs, the extent of seawater anoxia at those times is undefined and the causative processes remain unclear. Here we show how changes in seawater molybdenum isotope ratios (a proxy for seawater anoxia) during the Toarcian (Early Jurassic) OAE define the onset and expansion of oxygen deficient conditions. Our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically, broadly in line with precession-driven changes in [[delta].sup.13][C.sub.org]. Despite their intermittent occurrence over geological history, OAEs have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day. Keywords: Toarcian, Jurassic, molybdenum, oceanic anoxic event, carbon cycle.

Molybdenum isotopes in 20 molybdenite samples, dated by the Re-Os method and representing a range of geologic settings, show mass-dependent fractionation spanning 0.63[per thousand] per atomic mass unit (amu). Previous Mo isotope data for molybdenite reveal variations in fractionation of Keywords: molybdenum isotopes, molybdenite, paleoredox, Rayleigh fractionation, Re-Os ages, vapor transport.

The molybdenum hyperfine tensors and g-tensors of [Mo.sup.v] systems can be well reproduced by hybrid DFT methods. However it suffers from some limitations like, the parallel g-tensor component comes out insufficiently negative in treatments that include spin-orbit coupling only to leading order in perturbation theory.

Biimidazole and bis(amide)bipyridine molybdenum carbonyl complexes were prepared and their reactions with anions were studied. The neutral complexes [Mo[(CO).sub.4](N-N)] (1,2) and [MoCl([[eta].sup.3]-methylallyl)[(CO).sub.2](N-N) (3,4) were found to be insoluble due to intermolecular hydrogen bonding and [Mo([[eta].sup.3]-methylallyl)(CNBu)(C[O.sub.2])(N-N)]B[Ar'.sub.4] (5,6) displayed a high solubility in moderately polar organic solvents.

The N-N bond of dinitrogen at the FeMo cofactor is studied on the basis of density functional calculations. The strongly exothermic cleavage of the dinitrogen bond occurs, while a single nitrogen atom bridges the Fe atoms.

The synthesis and properties of metal--metal (MM) quadruply bonded compounds of molybdenum and tungsten in liquid crystalline phases are described. Covalently linked MM quadruply bonded complexes, dimers of dimers, are shown to give rise to mixed valence complexes upon oxidation and the degree of electron delocalization is shown to be correlated with the [M.sub.2][delta] bridge [pi] interactions. Class III behavior or complete delocalization is observed to [M.sub.2] to [M.sub.2] distances of up to 14 [Angstrom]. When the [M.sub.2] unit is attached to oligothiophenes via a carboxylate tether, the photophysical properties of the thienyl units are greatly modified due to [M.sub.2][delta]-thienyl [pi] conjugation and spin--orbit coupling. This leads to long-lived emissive states and electroluminescence in solid-state devices. mesogens | mixed valency

The dispersions of [Mo.sub.6][S.sub.3][I.sub.6] nanowires in various solvents are monitored by measuring their optical transmission as a function of time. The material can be purified by controlled sedimentation and thus the identification of the various phases is confirmed by x-ray photoelectron spectroscopy and scanning electron microscopy.

The acid-base reactivity of MS2(dmpe)2, where M = Mo and W and dmpe = Me2PCH2CH2PMe2 is examined. Consistent with its ready protonation, complex M=Mo is methylated, and the use of excess MeOTf gives [MoS(OTf)(dmpe)2](super +) and Me2S in a rare example of double alkylation at a sulfido ligand.

A new family of tetracarbonyl molybdenum(0) and tungsten(0) complexes based on new 6,6'-disubstituted-4,4'-bipyrimidine ligands was synthesized and characterized. The visible region of the absorption spectrum of each complex is dominated by a metal-to-ligand charge transfer band significantly lower in energy than the corresponding transition in 2,2'-bipyridine tetracarbonyl metal complexes. The 6,6'-substituents create a larger n-electronic system in the substituted bipyrimidines and are consequently better [pi] acceptors than even the parent 4,4'-bipyrimidine. The absorption bands are shifted bathochromically with a decrease in solvent polarity. Key words: molybdenum and tungsten, nitrogen ligands, tetracarbonyl metal complexes, absorption spectroscopy, electrochemistry. Resume : Une nouvelle famille de complexes de type tetracarbonyle de molybdbne(0) et tungstene(0), a base des 4,4'-bipyrimidine substituees dans les positions-6,6', a ete synthdtisde et caractdrisee. Le spectre d'absorption dans la region du visible de chaque compose indique un deplacement vers le rouge pour la bande de transfert de charge metal-ligand compare a celui du complexe tetracarbonyle de 2,2'-bipyridine. Ceci demontre une meilleure delocalisation du systeme [pi]-electronique darts la bipyrimidine substitude qui rend ces ligands des meilleurs accepteurs [pi]. Cette bande d'absorption est deplacee bathochromiquement avec la diminution de la polarite du solvant. Mots cles : molybdenum et tungsten, ligands azotes, complexes metal-tetracarbonyle, spectroscopie d'absorption, electrochimie.

Rapid palladium-catalyzed carbonylative cyclization reactions of 2-iodophenol with various alkynes have been carried out by the use of commercially available molybdenum hexacarbonyl as a convenient and solid carbon monoxide source. The reactions were conducted at 160 [degrees]C for 30 min with microwave heating in the presence of DIEA and DMAP in 1,4-dioxane, and afford the corresponding chromen-2-one derivatives in good yields. Key words: microwave, palladium, carbonylation, 2-iodophenol, chromen-2-one. Faisant appel a l'hexacarbonyle de molybdene disponible commercialement comme source solide et pratique de monoxyde de carbone, il est possible d'effectuer des reactions du 2-iodophenol avec de divers alcynes qui conduisent rapidement a des cyclisations accompagnees d'une carbonylation. Les reactions ont ete en 30 min par chauffage microonde a 160 [degrees]C, en presence de DIEA et de DMAP dans le 1,4-dioxane, et elles ont conduit aux chrom-2-enones correspondantes avec de bons rendements. Mots cles : microonde, palladium, carbonylation, 2-iodophenol, chrom-2-enone. [Traduit par la Redaction]

The direct oxidation of cysteine by [Mo(CN)8](super 3-) is studied using dipic as a Cu-catalysis inhibitor. The findings indicate that dipicolinic acid (dipic) is effective in suppressing the copper catalysis, thus enabling an examination of the direct oxidation of cysteine by [Mo(CN)8](super 3+).

A study is conducted to show that the iron-molybdenum (FeMO)-cofactor of the nitrogenase alpha-70(super lle) molybdenum-iron (MoFe) protein variant accumulates a novel S = 1/2 state that can be trapped during the reduction of protons to H(sub 2). The data does not favor any model involving protonation of sulfides, however it suggests that the intermediate contains two chemically equivalent bound hydrides.

Summarized here are our continuous studies of the last three decades concerning syntheses of new types of complexes learned from nitrogenase and their reactivites toward dinitrogen, nitriles, and alkynes. For Mo and W dinitrogen complexes with tertiary phosphine coligands, a variety of their intriguing reactivities have been demonstrated, and novel transformations of the [N.sub.2] ligands into numerous nitrogen-containing ligands and compounds have been developed. The C [equivalent to] N bond cleavage of certain nitriles also proceeds on the Mo site surrounded by tertiary phosphines. Stimulated by the sophisticated structure of the active site of nitrogenase, multinuclear metal--sulfur complexes have been synthesized in rational ways. New types of stoichiometric and catalytic reactions of alkynes have been found by using the thiolato-bridged diruthenium complexes and some cubane-type sulfido clusters containing a noble metal. Key words: nitrogen fixation, molybdenum and tungsten dinitrogen complexes, ruthenium thiolato complexes, metal sulfido clusters, nitriles, alkynes. Resume : Dans ce travail, on presente un Resume des etudes qui se poursuivent dans notre laboratoire et qui ont ete realisees depuis au moins trente ans sur des synthases de nouveaux types de complexes basees sur la facon de faire de la nitrogenase et sur leurs reactivites vis-a-vis du diazote, des nitriles et des alcynes. Pour les complexes du diazote avec le molybdene et le tungstene comportant des coligands de nature phosphine tertiaire, on a mis en evidence une variete de reactivites intrigantes et on a developpe de nouvelles transformations de ligands [N.sub.2] en de nombreux ligands et composes contenant de l'azote. Le clivage de la liaison C [equivalent to] N de certains nitriles procede au niveau d'atomes de molybdene entoures de phosphines tertiaires. Stimules par la structure sophistiquee du site actif de la nitrogenase, on a synthetise de facons rationnelles des complexes sulfur, s de metaux polynucleaires. On a aussi decouvert de nouveaux types de reactions stoechiometriques et catalytiques des alcynes en faisant appel e des complexes de diruthenium comportant des ponts thiolato et quelques agregats sulfido de type cubane contenant des metaux nobles. Mots cles : fixation de l'azote, complexes de diazote avec le molybdene et le tungstene, complexes thiolato du ruthenium, agregats sulfido metalliques, nitriles, alcynes. [Traduit par la Redaction]

Solid-state coordination chemistry of the oxomolybdate-organodiphosphonate/nickel-organoimine system is presented. A polyhedral representation of the structure of [{Ni3 (tpyprz)(sub 2)(H2O)(sub 2)}-(Mo5O15)(Mo2F2O4){O3P(CH2)(sub 3)PO3}(sub 2)] is shown.

Assembled complexes with highly controlled nuclearity and dimensionality are extensively investigated. Treatment of Pd2Cl2(CNC6H3Me2-2,6)4 with Mo2(O2CCF3)4 in dichloromethane afforded an infinite zigzag chain {[Pd2Cl2(CNC6H3Me(sub 2)-2,6)4]Mo2(O2CCF3)4]}(sub n), where two metal-metal bonded dinuclear Pd-Pd and Mo-Mo units were bridged by chloro atoms.

X-ray absorption spectra (XAS) at the Cl and S K edge and molybdenum (Mo) L edge are calculated at the TDDFT level for a series of dioxomolybdenum complexes LMoO2X (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate, X = Cl, SCH2Ph, OPh), which play an important role in modeling the catalytic cycle of the sulfite oxidase enzyme.

The synthesis of trinuclear magnetic building block of Mo3S7(dmit)(sub 3) is described. The potential of Mo3S7 cluster complex paves the way to an entirely new set of molecular conductors and/or magnets.

MoS(sub 2) nanostructures including hollow-cage fullerene-like particles, fibrous floccus, and spherical nanovesicles are synthesized by designed solution chemical reactions of Na(sub 2)MoO(sub 4) and sulfurization reagents. The electrochemical properties of annealed MoS(sub 2) samples are investigated as Mg(super 2+) ions showed better reversibly intercalation/deintercalation cycles in as-synthesized MoS(sub 2) nanostructures than in bulk MoS(sub 2) samples.

Synthesis of Mo-based complexes is described. Studies on the ability of polymer-bound chiral complexes to promote an assortment of asymmetric ring closing (ARCM) and ring-opening (AROM) metathesis reactions are described.

The synthesis and characterization of oxo-vanadium, oxo-molybdenum and the first examples of oxo-uranium complexes with 2-(4',4'-dimethyl-3'-4'-dihydroxazol-2'-yl)phenol and oxo-vanadium, manganese and cobalt complexes with a novel oxazine, 2-(5,6-dihydro-4H-1,3-oxazolinyl)phenol is described. It was seen that in all the reactions, benzaldehyde formed exclusively as the oxidation product.

Linkage isomers bridged oxamidate dianions are used for modifying electronic communication in dimolybdenum units. The results suggest that the pi interaction over the entire fused bicyclic chelating ring could be responsible for the metal-metal interaction and also indicates the presence of a strong electronic communication between the two linked dimetal units.

Reactions of terminal chloroaminophosphido complexes with [Co.sub.2](CO)s have been examined. The ruthenium phosphido complexes [Cp*Ru([CO).sub.2] {P(C1)TMP}] (1a) and [CpRu[(CO).sub.2] {P(C1)TMP}] (1b) (TMP = 2,2,6,6-tetramethyl-piperidinyl) react with [Co.sub.2] [(CO).sub.8] to form the cobalt cluster [[Co.sub.4][(CO).sub.7] [([micro]-CO).sub.3]{[[micro].sub.3]-P(TMP)}] (2) with complete transfer of the phosphinidene unit to cobalt. In contrast, the phosphido complex [Cp*Ru(CO)2{P(C1)N-i-Pr2}] (1c) affords the spiked-triangular cluster [Cp*Ru[Co.sub.3][(CO).sub.8] [([[micro].sub.3]-CO).sub.2]([[micro].sub.3]-PN-i-[Pr.sub.2])] (3), which retains the Cp*Ru unit upon reaction with [Co.sub.2][(CO).sub.8]. The molybdenum phosphido complex [CpMo[(CO).sub.2]{P(C1)TMP}] (4) reacts with [Co.sub.2][(CO).sub.8] to form cluster 2, while [Cp*Mo[(CO).sub.3] {P(C1)N-i-[Pr.sub.2]} ] (5) generates the mixed metal tetrahedral cluster [Cp*Mo[Co.sub.3][(CO).sub.5][([micro]-CO).sub.4] ([[micro].sub.3]-PN-i-[Pr.sub.2])] (6). Key words: phosphido, phosphinidene, cobalt, ruthenium, molybdenum, cluster.

The interactions of Y and Mo with NH(sub 3) can be rationalized in terms of attractive and repulsive interactions between the metal electrons and the lone pair of the ammonia. The studies showed that the binding energy indicates that the reaction of Y and Y(sub 2) is possible compared to Mo, and Mo(sub 2). The differences in the bonding are correlated with the difference in the molecular orbital occupation.

The growth of a submonolayer of metallic Mo on Au (11) by using scanning tunnel microscopy (STM) is studied. The results show the oxidation of Mo islands leading to their spreading proving that Mo clusters are either three-dimensional above or embedded in the surface of the gold substrate.

A series of potassium-promoted molybdenum catalysts (alkali/Mo molar ratio < 1) are characterized by probing the surface molybdenum species and the physical-chemical properties of the Si/Ti support to examine the effect of the alkali level on the surface characteristics of the support. The results revealed that with the addition of low levels of potassium distorted MoOx units, experiencing decreased Lewis acidity, could be more reactive towards electronegative Si-O(super -) support ligands on the Si/Ti 1:1 support.

Enantiopure TpMo(CO)(Sub 2)(pyridinyl) complexes are prepared using a scalable enzymatic kinetic resolution of the precursor to the molybdenum complex. It can function as a chiral scaffold for the enantiocontrolled synthesis of either 2,3,6-cis- or 2,6-cis-3- trans-trisubstituted piperidines.

A series of three new Mo-Sn clusters containing a [Mo3OS3Sn](super 6+) core are prepared by the reaction of [Mo(sub 3)(mu3-O)(mu-S)3](super 4+) type cluster complexes with SnCl2. Different configurations are observed according to the peripheral ligands.

A cluster model quantum chemical approach is used to study the electronic structure of Co in bimetallic sulphide catalysts Co/MoS(sub-2). On the basis of the calculations presented it is assumed that the active centre of sulphide Co--Mo catalysts include Co(III) atoms in a d(sup-6)-electronic configuration, which is stabilized by hydrogen species occluded in the catalyst bulk.

An attempt was made to characterize in-situ an Mo modified phosphoric rare earth-containing penta-sil zeolite catalyst using high-resolution solid-state MAS NMR, equipped with a newly designed device for conducting catalytic reactions. It shows good activity for methane dehydro-aromatization in the absence of oxygen.

A new bimetallic complex of nickel(II) coordinated to a molybdenum-containing metalloligand is synthesized that forms a helical chain through hydrogen bonding and shows spontaneous resolution upon crystallization. The obtained compound is also a potential single-source precursor for NiO.2Mo[O.sub.3].

Abstract -- The complexation of molybdenum(VI) with 2-hydroxy-5-tertbutylphenol-2'-methylazobenzene was studied by atomic absorption spectrometry and spectrophotometry. Optimum conditions for complex formation and extraction were found. The ratio of components in [...]

Abstract -- The complexation of molybdenum(VI) with Bromopyrogallol Red in the presence of the nonionic surfactant Triton X-114 is studied spectrophotometrically. A mixed-ligand complex is formed with the component ratio [...]

Mo(super VI)(S2C6H4) reacts cleanly and completely with H(sub 2)O in THF to afford [H(sub 3)](super +)[Mo(super V)(S2C6H4)3](super -1). The Mo(super VI)(S2C6H4)3 reduction is acceralated by the presence of PPh3 and affords OPP3.

A ID rope-ladder shaped Cu(II)-Mo(V) assembly bridged by CN ligands was synthesized. The characterization studies were conducted by using X-ray crystallography and magnetometry.

A new self contained molecular oxide [(IMo7O26)(sub 2)](super 6-) has been synthesized. The novel yet self contained nature of the structure suggests the existence of a new class of molecular oxides of related structures.

The synthesis and structure of the first Mo/Fe/S/BH4 cluster is reported. A synopsis of the solution characterization as well as the reactivity of this cluster is also presented.

The stoichiometry of sputtered molybdenum oxide films that can be changed from oxygen deficient to oxygen rich is studied. The study shows that the excess oxygen fraction in these films is present in physically trapped state as well as a chemically bonded state.

A study was conducted to systematically explore the assembly of [Mo.sub.2][([O.sub.2]C-).sub.4]-based metal-organic molecular architectures structurally controlled by the bridging angles of rigid organic linkers. The results revealed that the shape and size of the resulting molecular architecture could be controlled by tuning the bridging angle and size of the linker, respectively.

The article presents a new approach, which employs the molybdenum seed layers for the enhancement of the nucleation of smooth, as well as the dense nanocrystalline diamond (NCD) films. The coating of the films via Si substrate is shown to be extremely beneficial for enhancing the nucleation kinetics of the diamonds on the films.