A Three‐Dimensional MnII‐[MoIII(CN)7]4– Ferrimagnet Containing Formate as a Second Bridging Ligand

Self‐assembly of the [Mo(CN)₇]^4– anion and the Mn²⁺ ion in the aqueous solution containing ammonium formate results in a new coordination polymer, {(NH₄)₃[(H₂O)Mn₃(HCOO)][Mo(CN)₇]₂·4H₂O}_n. Single crystal X‐ray analysis revealed a very complicated three‐dimensional (3D) framework, where both the [Mo(CN)₇]^4– and the formate anions act as bridges between the Mn^II centers. Magnetic measurements revealed that this compound displays ferrimagnetic ordering below 70 K. Competing antiferromagnetic interactions between the spin carriers might lead to spin frustration and non‐linear alignment of the magnetic moments. Specifically, this compound is the first mixed [Mo(CN)₇]^4–/HCOO^– bridged molecule magnet.     

X‐ray Magnetic Circular Dichroism Spectroscopy Applied to Nitrogenase and Related Models: Experimental Evidence for a Spin‐Coupled Molybdenum(III) Center

Nitrogenase enzymes catalyze the reduction of atmospheric dinitrogen to ammonia utilizing a Mo‐7Fe‐9S‐C active site, the so‐called FeMoco cluster. FeMoco and an analogous small‐molecule (Et₄N)[(Tp)MoFe₃S₄Cl₃] cubane have both been proposed to contain unusual spin‐coupled Mo^III sites with an S(Mo)=1/2 non‐Hund configuration at the Mo atom. Herein, we present Fe and Mo L₃‐edge X‐ray magnetic circular dichroism (XMCD) spectroscopy of the (Et₄N)[(Tp)MoFe₃S₄Cl₃] cubane and Fe L_2,3‐edge XMCD spectroscopy of the MoFe protein (containing both FeMoco and the 8Fe‐7S P‐cluster active sites). As the P‐clusters of MoFe protein have an S=0 total spin, these are effectively XMCD‐silent at low temperature and high magnetic field, allowing for FeMoco to be selectively probed by Fe L_2,3‐edge XMCD within the intact MoFe protein. Further, Mo L₃‐edge XMCD spectroscopy of the cubane model has provided experimental support for a local S(Mo)=1/2 configuration, demonstrating the power and selectivity of XMCD.     

Formation and electrocatalytic properties of Pd deposits on Mo obtained by galvanic displacement

A Pd-Mo electrocatalytic system was obtained by forming palladium particles on the Mo surface that contacted a PdCl₂ solution under open-circuit conditions. The state of palladium on the electrode surface depended on the contact displacement time. Palladium particles 5–10 nm in size formed on the surface of the Pd(Mo) electrode after palladium deposition for 1 min. The specific rates of formic acid oxidation on the Pd(Mo) electrode were smaller than those on the Pd/Pt electrode. On the Pd(Mo) electrode, anode currents of methanol oxidation were recorded at a potential of 0.4 V. The difference in the effects of the Mo substrate on the activity of Pd particles in the electrooxidations of HCOOH and CH₃OH was explained by the difference in the mechanisms of these reactions.     

Single‐Crystal X‐Ray Diffraction Study of Pressure and Temperature‐Induced Spin Trapping in a Bistable Iron(II) Hofmann Framework

High‐pressure single‐crystal X‐ray diffraction has been used to trap both the low‐spin (LS) and high‐spin (HS) states of the iron(II) Hofmann spin crossover framework, [Fe^II(pdm)(H₂O)[Ag(CN)₂]₂?H₂O, under identical experimental conditions, allowing the structural changes arising from the spin‐transition to be deconvoluted from previously reported thermal effects.     

MoO3, WO3 Single and Binary Oxide Prepared by Sol-Gel Method for Gas Sensing Applications

MoO₃, WO₃ single and Mo/W binary compounds at different Mo/W atomic percentages were deposited by sol-gel spin coating technique on Si/Si₃N₄ substrates provided with Pt interdigital electrodes and annealed at 450°C for 1 h. Films were characterized by SEM, grazing incidence XRD and XPS techniques. Electrical responses to different gases were obtained by exposing the films to 30 ppm CO and 1 ppm NO₂. Increasing the Mo/W content the selectivity to NO₂ is enhanced. Gas responses resulted to be influenced by the Mo/W weight ratio, films morphology and amount of crystalline phases.     

Oxidation of methanol on Pt(Mo) electrodes obtained using galvanic displacement method

The electrocatalytic Pt-Mo system was obtained by formation of platinum particles on the Mo surface under its contact with PtC₆²⁻ (PtCl₄²⁻) under the open circuit conditions. Cyclic voltammograms of the obtained Pt(Mo) electrodes feature well pronounced peaks of hydrogen adsorption and desorption on Pt particles. Nonuniform platinum distribution across the electrode surface was found. Pt(Mo) electrodes showed a higher specific activity in the reaction of methanol oxidation in the potential range of 0.35–0.45 V (RHE) as compared to Pt/Pt.     

Polymere Thiolatokomplexe [M(SPh)3]∞ der Metalle Molybdän,Wolfram, Eisen und Ruthenium mit linearen Metallketten. Synthese und Struktur von (OC)3Fe(SPh)3Fe(SPh)3Fe(CO)3 · 2(CH3)2CO

Polymeric Thiolato Complexes [M(SPh)₃]∞ of the Metals Mo, W, Fe, and Ru with Linear Metal Chains. Synthesis and Crystal Structure of (OC)₃Fe(SPh)₃Fe(SPh)₃Fe(CO)₃ · 2(CH₃)₂CO At high temperature the reaction of the metal carbonyls Mo(CO)₆, W(CO)₆ and Fe(CO)₅ with S₂Ph₂ (Ph = C₆H₅) yields the polymeric complexes [M(SPh)₃]∞. Similarly [Ru(SPh)₃]∞ can be obtained from ruthenium(III) acetylacetonate and HSPh. At room temperature under UV-irradiation Fe(CO)₅ reacts with S₂Ph₂ to form the oligomeric complex (OC)₃Fe(SPh)₃Fe(SPh)₃Fe(CO)₃. The polymeric complexes [M(SPh)₃]∞ (M = Mo, W, Fe, Ru) are composed of linear chains with bridging SPh-ligands between the metal atoms. Of these complexes [Fe(SPh)₃]∞ is paramagnetic, whereas the others exhibit antiferromagnetic behaviour. The spin coupling is presumably connected with the formation of metal pairs, resulting in alternating shortened and extended distances in the metal chain. The oligomeric complex (OC)₃Fe(SPh)₃Fe(SPh)₃Fe(CO)₃ crystallizes triclinic in the space group P1 with z = 2. It has almost the symmetry D_3d with a linear arrangement of the Fe atoms. The paramagnetism of Fe₃(CO)₆(SPh)₆ can be explained by a d⁶ high spin configuration of the central atom and low spin behaviour of the two other Fe atoms, which are bonded to CO.     

Enzymatic and catalytic reduction of dinitrogen to ammonia: Density functional theory characterization of alternative molybdenum active sites

We used density functional calculations to model dinitrogen reduction by a FeMo cofactor containing a central nitrogen atom and by a Mo‐based catalyst. Plausible intermediates, reaction pathways, and relative energetics in the enzymatic and catalytic reduction of N₂ to ammonia at a single Mo center are explored. Calculations indicate that the binding of N₂ to the Mo atom and the subsequent multiple proton–electron transfer to dinitrogen and its protonated species involved in the conversion of N₂ are feasible energetically. In the reduction of N₂ the Mo atom experiences a cycled oxidation state from Mo(IV) to Mo(VI) by nitrogenase and from Mo(III) to Mo(VI) by the molybdenum catalyst, respectively, tuning the gradual reduction of N₂. Such a wide range of oxidation states exhibited by the Mo center is crucial for the gradual reduction process via successive proton–electron transfer. Present results suggest that the Mo atom in the N‐centered FeMo cofactor is a likely alternative active site for dinitrogen binding and reduction under mild conditions once there is an empty site available at the Mo site. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

POM‐Catalyzed In Situ Ligand Synthesis for the Construction of Metal Complexes and Their Use in the Formation of Coordination Polymers

Six organic–inorganic hybrid materials were synthesized by the in situ oxidation of neocuproine by using MoO₃/Na₂MoO₄ as the catalyst in the presence of Cu(NO₃)₂. The crystal structures of Mo8‐Cu4‐PHEN and Mo8‐Cu2‐5(2PIC) are composed of [Mo₈O₂₆]^4? polyoxometalate (POM) units, whereas the crystal structure of Mo6‐Cu‐COPHEN is composed of a [Mo₆O₁₉]^2? POM unit; both POM units could be considered as the active form of the catalyst. Reaction of the hybrid materials with 1,3,5‐benzenetricarboxylic acid (BTC) resulted in the formation of two different coordination polymers (CPs) under different reaction conditions. These CPs, depending on their structural attributes, exhibit distinct differences in the adsorption of H₂, CO₂, and water. The use of 2‐methylpyridine instead of neocuproine does not give any oxidation products under the same reaction conditions due to the incorrect positioning of the methyl group with respect to the Cu^II center.     

Preparation and properties of molybdenum and tungsten dinitrogen complexes : `XVI. Electrochemical properties of tungsten and molybdenum diazoalkane complexes

Diazoalkane complexes of type [MF(NNCRR′)(dpe)₂][BF₄] (M = Mo or W; dpe = Ph₂PCH₂CH₂PPh₂), which are easily derived from bis(dinitrogen) complexes [M(N₂)₂(dpe)₂], undergo consecutive one- and two-electron oxidations and reductions under voltammetric conditions at a platinum electrode. The ESR spectra of the species generated by the controlled potential electrolysis show that primary oxidation occurred on the metal atom (M = Mo) and reduction on the two nitrogen atoms in the diazoalkane ligands (M = Mo or W).     

Elektronenreiche übergangsmetallkomplexe : IV. Dien-bis(phosphin)-molybdändicarbonyle

Dienes can replace the acetonitrile in (CH₃CN)₂Mo(PBu₃)₂,(CO)₂ or acetoni- trile and the one phosphine trans to the CO group in (CH₃CN)Mo(PBu₃)₃(CO)₂ under mild conditions. IR-, H NMR, ¹³C NMR and electronic spectra of the new (diene)Mo(PBu₃)₂(CO)₂ complexes are discussed and compared with similar compounds of other transition metals.     

Ligand hyperfine coupling in Mo(V) oxyhalide complexes

For a series of Mo(V) oxyhalide complexes MoOL ₅ ^2? (L = F, Cl, Br, I), interpretation of the ligand hyperfine coupling parameters (A ^L tensor components) is considered. The role of spin polarization is elucidated and the effect of charge transfer states is taken into account. The A ^L tensor components were calculated using the covalency parameters derived from experimental EPR and optical spectroscopy data for compounds under study (inverse problem of EPR spectroscopy).     

Transition metal promoted reactions : IV. Thermolysis of cyclopentadienone dimers and related compounds with group VI metal carbonyl

Thermal decomposition of dicyclopentadienone in the presence of M(CO)₆ (M = Cr, Mo, W) yields indanone. 2-Bromocyclopentadienone dimer, on the other hand, affords 4-bromoindanone under the same conditions. Nocorresponding organometallic complexes were isolated. The mechanismof this reaction is discussed.     

Mo(CO)6-promoted facile deoxygenation of α,β-epoxy ketones and α,β-epoxy esters

Deoxygenation of α,β-epoxy ketones and α,β-epoxy esters is accomplished in high yields under mild and neutral conditions by the use of Mo(CO)₆.     

Electron spin resonance study on UV-irradiated single crystal of (NH3iPr)6[Mo8O28(CHO)2] · 2H2O

EPR study on UV-irradiated single crystal of (NH₃iPr)₆ [Mo₈ O₂₈(CHO)₂]·2H₂O was carried out at room temperature. Three sets of EPR lines were observed. Spectra I and II are attributed respectively to paramagnetic Mo (V) centre (A) and (B). Line III may be assigned to an unstable-paramagnetic centre. Using the least-squares-fitting method to calculate the Hamiltonian parameters, we got the accurate principal values of g, hyperfine A_MO and ligand hyperfine A_H tensors, as well as-the direction cosines of their principal axes with respect to experimental coordinate system (xyz). The electron spin density was calculated from A value. The results showed that the unpaired electron occupies 4d orbital of molybdenum which appreciably contributes to the molecular orbital and the mechanism of direct spin coupling between the unpaired spin orbital of molybdenum and hydrogen orbital.     

Differential-pulse voltammetric determination of molybdenum in nitrate medium in the presence of 8-hydroxyquinoline

The determination of Mo(VI) by differential-pulse voltammetry based on catalytic currents in nitrate medium is described. The existence of catalytic currents in the system Mo(VI)NO₃^? in the presence of 8-hydroxyquinoline was proved by various polarographic techniques. The optimum background electrolyte is 20 ml 0.5 M KNO₃?0.005 M HNO³ with the addition of 1 ml of 1 × 10^?2 M 8-hydroxyquinoline. The detection limit is 7 × 10^?10 M under these conditions. Cr(VI), Cu(II), Cd(II) and Pb(II) interfere when present at higher concentrations then Mo(VI) and W(VI) interferes at an equal concentration to Mo(VI). The method was successfully used in analyses of environmental samples.     

Determination of the nuclear structure and spin density distribution in the cyano-bridged molecular based magnet K2Mn3(H2O)6[Mo(CN)7]2·6 H2O

This article details the local spin density determination in the cyano-bridged, two-dimensional, molecular based magnet K₂Mn₃(H₂O)₆[Mo(CN)₇]₂·6 H₂O (T_c = 39 K). The crystal structure, determined at room temperature by X-ray diffraction, was redetermined at 50 K using unpolarised neutron diffraction. The importance of intermolecular hydrogen-bonding interactions is clearly demonstrated in this study, previously characterised with X-rays. The local spin density was determined from polarised neutron diffraction data at 4 K with an applied field of 3 T. Positive spin densities were observed on the manganese sites, consistent with high-spin d⁵ ions in octahedral fields, whilst a negative spin density was found on the molybdenum sites, signifying delocalisation onto the cyano ligands. The alternating sign of the spin populations on the metal sites, suggests that the primary Mo^III–Mn^II interactions are antiferromagnetic in nature and the delocalisation onto the cyano-bridges clearly demonstrates the role of the ligand bridges in the magnetic exchange pathway.     

The Influence of Defects on Mo‐Doped TiO2 by First‐Principles Studies

TiO₂ doped with transition metals shows improved photocatalytic efficiency. Herein the electronic and optical properties of Mo‐doped TiO₂ with defects are investigated by DFT calculations. For both rutile and anatase phases of TiO₂, the bandgap decreases continuously with increasing Mo doping level. The 4d electrons of Mo introduce localized states into the forbidden band of TiO₂, and this shifts the absorption edge into the visible‐light region and enhances the photocatalytic activity. Since defects are universally distributed in TiO₂ or doped TiO₂, the effect of oxygen deficiency due to oxygen vacancies or interstitial Mo atoms is systemically studied. Oxygen vacancies associated with the Mo dopant atoms or interstitial Mo will reduce the spin polarization and magnetic moment of Mo‐doped TiO₂. Moreover, oxygen deficiency has a negative impact on the improved photocatalytic activity of Mo‐doped TiO₂. The current results indicate that substitutional Mo, interstitial Mo, and oxygen vacancy have different impacts on the electronic/optical properties of TiO₂ and are suited to different applications.     

Molybdenum-mediated cyclocarbonylation of 1-ethynyl-2-allenylbenzenes to 1H-cyclopenta[a]inden-2-ones

Although 1-ethynyl-2-allenylbenzenes readily undergo Myers-Saito or Schmittel cyclization under mild conditions, cyclocarbonylation of these moieties to 1H-cyclopenta[a]inden-2-ones proceeds smoothly using suitable molybdenum carbonyl reagents, with Mo(CO)₃(CH₃CN)₃ being the most efficient. The yields of desired bicyclic ketones were up to 87-93%.     

Sorption and separation of some elements of nuclear importance using Chelex-100

Chelex-100, in the anionic form has been studied for its ability to perform selective separation and concentration of some metal ions of nuclear importance from mineral acid solutions. The sorption behavior of Zr(IV)–Nb(V), Mo(VI), Tc(VII), Te(IV) and U(VI) from solutions of hydrochloric and sulphuric acids on Chelex-100 has been studied under static and dynamic conditions. Mo(VI) and Tc(VII) have been concentrated on the resin from hydrochloric or sulphuric acid solutions at low acidities probably, as the anions MoO ₄ ^2– and TcO ₄ ^– , respectively. Te(IV) has been isolated from hydrochloric acid solutions of normalities 6 in the form of the anionic chloro complex TeCl ₆ ^2– . Optimum conditions for elution and separation of Mo(VI), Tc(VII), Te(IV) and U(VI) were recommended.