MoV Ions Research Articles

Organically Functionalized Mixed-Valent Polyoxo-30-molybdate Wheel and Neutral Tetramolybdenum(V) Oxo Cluster.

The first organofunctionalized mixed-valent polyoxo-30-molybdate wheel, [MoVI18MoV12O84{AsO2(CH3)2}18]18- (Mo30), was synthesized in aqueous, mildly acidic conditions, and upon further acidification, the neutral tetramolybdenum(V) oxo cluster [MoV4O8{AsO2(CH3)2}4] (Mo4) was obtained. Single-crystal X-ray diffraction (XRD) revealed that Mo30 comprises 18 MoVI and 12 MoV ions arranged in a cyclic fashion with alternating {MoV2} and {MoVI3} groups, which are capped by 18 dimethylarsinate ligands, resulting in a novel polyoxo-30-molybdate wheel with a central cavity of ∼1.5 nm. On the other hand, Mo4 has a distorted-cubic structure, with the corners of the cube being occupied by alternating MoV ions and oxo ligands. The compounds were characterized in solution by 1H and 13C NMR and UV-vis spectroscopy and in the solid state by X-ray photoelectron spectroscopy and powder XRD. Mo30 represents a novel type of polyanionic cycle with manyfold possibilities regarding host-guest chemistry.

Temperature-dependent formation of redox sites in molybdenum trioxide studied by electron paramagnetic resonance spectroscopy

The formation and qualification of redox sites in transition metal oxides are always the active fields related to electronics, catalysis, sensors, and energy-storage units. In the present study, the temperature dependence of thermal reduction of MoO3 was surveyed at the range of 350 °C to 750 °C. Upon reduction, the formed redox species characterized by EPR spectroscopy are the MoV ion and superoxide anion radical (O2−) when the reduction was induced at the optimal temperature of 300−350 °C. When heating-up from 350 °C, the EPR signals started to decline in amplitude. The signals in the range of 400−450 °C decreased to half of that at 350 °C, and then to zero at ∼600 °C. Further treatment at even higher temperature or prolonged heating time at 500 °C caused more reduction and more free electrons were released to the MoO3 bulk, which results in a delocalized means similar to the anti-ferromagnetic coupling. These data herein are helpful to prepare and study the metal-oxide catalysts.

Protein-Assisted Formation of Molybdenum Heterometallic Clusters: Evidence for the Formation of S2MoS2-M-S2MoS2 Clusters with M = Fe, Co, Ni, Cu, or Cd within the Orange Protein.

The Orange Protein (ORP) is a small bacterial protein, of unknown function, that harbors a unique molybdenum/copper (Mo/Cu) heterometallic cluster, [S2MoVIS2CuIS2MoVIS2]3-, noncovalently bound. The apo-ORP is able to promote the formation and stabilization of this cluster, using CuII- and MoVIS42- salts as starting metallic reagents, to yield a Mo/Cu-ORP that is virtually identical to the native ORP. In this work, we explored the ORP capability of promoting protein-assisted synthesis to prepare novel protein derivatives harboring molybdenum heterometallic clusters containing iron, cobalt, nickel, or cadmium in place of the "central" copper (Mo/Fe-ORP, Mo/Co-ORP, Mo/Ni-ORP, or Mo/Cd-ORP). For that, the previously described protein-assisted synthesis protocol was extended to other metals and the Mo/M-ORP derivatives (M = Cu, Fe, Co, Ni, or Cd) were spectroscopically (UV-visible and electron paramagnetic resonance (EPR)) characterized. The Mo/Cu-ORP and Mo/Cd-ORP derivatives are stable under oxic conditions, while the Mo/Fe-ORP, Mo/Co-ORP, and Mo/Ni-ORP derivatives are dioxygen-sensitive and stable only under anoxic conditions. The metal and protein quantification shows the formation of 2Mo:1M:1ORP derivatives, and the visible spectra suggest that the expected {S2MoS2MS2MoS2} complexes are formed. The Mo/Cu-ORP, Mo/Co-ORP, and Mo/Cd-ORP are EPR-silent. The Mo/Fe-ORP derivative shows an EPR S = 3/2 signal (E/D ≈ 0.27, g ≈ 5.3, 2.5, and 1.7 for the lower M= ±1/2 doublet, and g ≈ 5.7 and 1.7 (1.3 predicted) for the upper M = ±3/2 doublet), consistent with the presence of either one S = 5/2 FeIII antiferromagnetically coupled to two S = 1/2 MoV or one S = 3/2 FeI and two S = 0 MoVI ions, in both cases in a tetrahedral geometry. The Mo/Ni-ORP shows an EPR axial S = 1/2 signal consistent with either one S = 1/2 NiI and two S = 0 MoVI or one S = 1/2 NiIII antiferromagnetically coupled to two S = 1/2 MoV ions, in both cases in a square-planar geometry. The Mo/Cu-ORP and Mo/Cd-ORP are described as {MoVI-CuI-MoVI} and {MoVI-CdII-MoVI}, respectively, while the other derivatives are suggested to exist in at least two possible electronic structures, {MoVI-MI-MoVI} ↔ {MoV-MIII-MoV}.

An Unprecedented M-O Cluster Constructed from Nanosized {[C5NH5]9[H31MoV12O24CoII12(PO4)23(H2O)4]}2- Anions Exhibiting Interesting Nonlinear-Optical Properties.

A novel high-nuclear nanosized cluster modified by conjugated organic ligands (pyridine and imidazole), [C5NH5]8[C3H5N2]2{[C5NH5]9[H31Mo12O24Co12(PO4)23(H2O)4]}·12H2O (1), has been successfully isolated under hydrothermal conditions and structurally characterized. Compound 1 consists of 12 CoII and 12 MoV ions linked by 23 {PO4} groups, exhibiting unprecedented nanosized ship-shaped clusters. The magnetic measurements reveal that compound 1 exhibits dominant antiferromagnetic interactions. Additionally, pyridine and imidazole ligands enhance the delocalized electron effects of clusters, and the third-order nonlinear-optical response of compound 1 is excellent.

Synthesis, crystal structures, and magnetic properties of three Mo(V)–Ln(III) (Ln = Ho, Er, Tm) magnetic chains based on [Mo(CN)8]3-

Complexes 1–3 with general formula [Ln(tmphen)2(DMF)2Mo(CN)8]∞ (Ln = Ho(1), Er(2) and Tm(3)) have been prepared by reaction of Cs3[Mo(CN)8]·4H2O and Ln(NO3)3·6H2O in the presence of the tmphen blocking ligand (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline), and characterized by IR, elemental analysis, single crystal X-ray diffraction and magnetic measurements. The structural determination reveals that complexes 1–3 consist of 1D chains, in which [LnIII(tmphen)2(DMF)2]3+ and [MoV(CN)8]3− ions are linked in an alternating fashion. Furthermore, two adjacent 1D chain are linked by π–π interaction between the benzene and pyridine rings and hydrogen bonds to form a supramolecular three-dimensional framework. Investigation of the magnetic properties of complexes 1–3 reveals antiferromagnetic coupling interaction exists between heavy LnIII (HoIII, ErIII and TmIII) and MoV ions.

Nine cyanide-bridged bimetallic magnetic chains derived from octacyanomolybdate(v) and lanthanide(iii) building blocks

The reactions of octacyanometallates [MoV(CN)8]3− and lanthanide ions in the solution of DMF (DMF = N,N-dimethylformamide) have yielded nine bimetallic coordination polymers: [LnIII(DMF)6MoV(CN)8]∞ [Ln = Pr(1), Nd(2), Sm(3), Eu(4), Gd(5), Ho(6), Er(7), Tm(8), Yb(9)]. All the coordination polymers consist of one-dimensional chains, in which [LnIII(DMF)6]3+ and [MoV(CN)8]3− ions link each other in an alternating fashion through the cyano-bridged coordination bonds. The variable-temperature magnetic susceptibility studies reveal the ferromagnetic interactions between LnIII and MoV ions in compounds 3 and 4, while antiferromagnetic interactions are found in compounds 1, 2, and 5–9.

A Bimetallic Chain Based on [Mo(CN)8]3− and Er3+ Ions as Building Blocks: Synthesis and Magnetic Properties

A novel bimetallic 4d-4f complex, [ErIII(DMF)4(H2O)2][MoV(CN)8]·i-C3H7OH·4H2O (1) (DMF = N,N′-dimethylformamide), has been synthesized and structurally characterized. The crystalline analysis shows that the build up of 1D zigzag-like chains produces complex 1, which is the first structurally characterized example of 1D structure based on the [Mo(CN)8]3− and Er3+ ions as building blocks. Complex 1 crystallizes in monoclinic system of space group P21/n, with a = 12.031(6), b = 16.027(7), c = 20.263(9) A, β = 105.711(6)o and Z = 4. Magnetic measurements confirm that 1 presents probably a ferromagnetic interaction between the MoV and ErIII ions.

Tetraaquatetrakis(4,4′-bipyridine dioxide-κO)terbium(III) octacyanidomolybdate(V)

In the title compound, [Tb(C10H8N2O2)4(H2O)4][Mo(CN)8], both metal atoms are eight-coordinated. The TbIII atom displays a dodecahedral geometry, while the MoV ion exhibits a distorted square-anti­prismatic geometry. The Tb atoms are located on a special position of site symmetry , whereas the Mo atoms are located on a twofold rotation axis. The cations are linked by O—H⋯O hydrogen bonds.

Multidimensional frameworks constructed from Keggin-type heteropoly blue of molybdenum–tungsten cluster

The reaction of polyoxometalate anion [GeW11O39]8− with the complex anion [MoV2O4(H2O)2(ox)2]2− in the presence of CuCl2·2H2O and DMF (DMF = N,N-dimethyl formamide) at 85 °C in aqueous solution produces both a two-dimensional heteropoly blue H2[α-GeW10MoV2O40][Cu(DMF)3H2O]2·5H2O (1) and a three-dimensional heteropoly blue H4[α-GeW10MoV2O40]2 [CuK2(DMF)6] [K4(DMF)6] (2), which demonstrates that different molar ratio of W : Cu in the reaction could conduct different multidimensional structures of 2D and 3D. The magnetic investigation of the two compounds in temperature range from 300 K to 2 K indicated the presence of strong antiferromagnetic interactions related with the two MoV ions in these two compounds.

In Rhodobacter sphaeroides respiratory nitrate reductase, the kinetics of substrate binding favors intramolecular electron transfer.

The respiratory nitrate reductase (NapAB) from Rb. sphaeroides is a periplasmic molybdenum-containing enzyme which belongs to the DMSO reductase family. We report a study of NapAB by protein film voltammetry (PFV), and we present the first quantitative interpretation of the complex redox-state dependence of activity that has also been observed with other related enzymes. The model we use to fit the data assumes that binding of substrate partly limits turnover and is faster and weaker when the Mo ion is in the V oxidation state than when it is fully reduced. We explain how the presence in the catalytic cycle of such slow chemical steps coupled to electron transfer to the active site decreases the driving force required to reduce the MoV ion and makes exergonic the last intramolecular electron-transfer step (between the proximal cubane and the Mo cofactor). Importantly, comparison is made with all Mo enzymes for which PFV data are available, and we emphasize general features of the energetics of the catalytic cycles in enzymes of the DMSO reductase family.

Spectrosopic and paramagnetic properties of molybdenum oxyhydroxide films electrochemically formed from the Keggin-type (PMo12O40)3− complex

Molybdenum-containing films electrochemically deposited from an aqueous solution of 12-molybdphosphate (PMo12O40)3− (denoted as PMo12) have been characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and electron spin resonance (ESR) techniques. XPS and FTIR data indicate that electrolysis of PMo12 leads to the formation of Mo–O–Mo linkage by condensation of the polyanions accompanied by decomposition of the phosphate moiety. The ESR spectrum of the deposited film exhibits an asymmetric signal with g ∼1.92, indicative of pentavalent molybdenum (d1). The feature of this signal is close to that for a MoV ion in the amorphous MoO3 phase, but not in the PMo12 framework. It is therefore suggested that the deposited film no longer has the Keggin structure PMo12, but consists of a continuous structure containing molybdenum oxide.

Crystal Structure and EPR Spectra of cis‐Dioxo‐molybdenum(V) Complex with o‐Aminophenol

AbstractThe paramagnetic cis‐dioxo‐molybdenum(V) complex, [NH2CH2CH2NH3]3[MovO2(HNC6H4O)2] was obtained by the reaction of tetra‐butyl ammonium β‐octamolybdate with o‐aminophenol and ethylenediamine in the mixed solvent of CH3OH and CH3CN, and characterized by IR, NMR, EPR spectroscopy and X‐ray diffraction analysis. The determination of single crystal X‐ray analysis revealed that the central Mov ion metal center exhibits distorted octahedral coordination with cis‐dioxo o‐aminophenol. The EPR spectra of both the complex and flavoenzyme show similarly. Thus it suggests that the complex anion [MovO2(HNC6H4O)2]3‐ and flavoenzyme have related structure feature.

Catalytic Properties of Silica-supported 12-Molybdophosphoric Acid in the Conversion of 2-Propanol

A technical silica gel was impregnated with a solution of the titled heteropoly acid (1–20 w/w%) and calcined at 400, 600 or 800 °C. Dehydration of the alcohol generally increased with the loaded acid, and decreased almost linearly with the reaction temperature (360–260°C). The best alcohol decomposition was achieved over the 600°C-calcined catalysts when over 90% conversion to propene was attained. The apparent activation energies decreased with the degree of loading and attained a value of 22 kJ/mol on the 600°C-calcined 20% HPMo-supported catalyst (half that on the solids calcined at 400°C and 800°C). The catalytic dehydration cannot be described by means of a proton-involved mechanism on the severely treated catalysts at ≥600°C. An outer surface mechanism might be effective involving terminal oxygens and MoV ions.

Exchange-coupled CrV and MoV ions on the surface of CrO x /ZrO2 and MoO x /ZrO2 : an electron paramagnetic resonance study

Samples with different Cr or Mo loading have been prepared by contacting the ZrO2 support with CrO3 solutions at pH = 1 (Cr content 0.05–5 wt.%) or (NH4)6Mo7O24 solutions at pH = 8 (Mo content 0.05–7 wt.%). In CrOx/ZrO2 samples heated with O2 at 773 K, a weak line at 1642 G is observed in the EPR spectra together with a strong signal due to mononuclear CrV species (53Cr). Analogously, in MoOx/ZrO2 samples heated with O2 at 773 K and reduced with H2 at 673–773 K, a weak line at 1674 G is detected together with a strong signal of mononuclear MoV(95Mo). The two half-field signals (1642 and 1674 G, respectively) are substantially broader in the samples enriched with 53Cr and 95Mo because of hyperfine interactions, whose structure is not, however, resolved. These lines arise from surface species as shown by experiment with O2. Relying also on chemical evidence (reversibility of the species in redox experiments), the two weak lines are assigned to the half-field transition of the state S= 1 of exchange-coupled CrV and MoV ions on the surface of ZrO2. It is suggested that the lines arise from isolated pairs. From the position of the line: (i) the D-term of the pair, (ii) the distance between ions in the pair and (iii) the probability of the half-field transition, are calculated.For both CrV and MoV, the concentration of the isolated mononuclear species and that of the isolated pairs measured by EPR are found to be in agreement with the corresponding values calculated on the assumption of a random distribution of Cr (or Mo) on the ZrO2 surface.

ChemInform Abstract: Spectroscopic Characterization of a Molybdena/Silica System Photoreduced in a Carbon Monoxide Atmosphere.

AbstractDie CO‐Adsorption des bei 823 K mit H2 reduzierten MoO3/SiO2‐Systems wird durch IR‐, UV‐ VIS‐ und ESR‐Techniken untersucht, wodurch die Bildung von Mo(V)‐ und Mo(IV)‐Spezies aufgezeigt wird.

Interaction of hydrogen chloride with a molybdena–silica catalyst

The interaction of HCl with a molybdena–silica catalyst has been investigated using e.p.r. and infrared spectroscopy. Exposure of reduced catalysts to HCl at room temperature causes a large (up to 20-fold) increase in the amount of MoV detected by e.p.r. which is reversed on subsequent outgassing. The accompanying changes in g- and the 95Mo hyperfine-tensor components indicate that chloride ions replace oxide ions in the coordination sphere of MoV, and the increase in MoV spin concentration is attributed to substitution of bridging oxide ligands between magnetically coupled MoV ions. Oxidized catalysts are reduced by exposure to HCl. The reaction of HCl with molybdena–silica is compared with that previously reported with molybdena–alumina catalysts.

X-Ray Structures of Di-μ-oxo, μ-Oxo-μ-thio-, and Di-μ-thio-μ-[(R)propylenediaminetetraacetato]-bis[oxomolybdate(V)] Ions

Abstract The crystal structures of Na2[Mo2O4(R-pdta)]·3H2O (1), Na2[Mo2O3S(R-pdta)]·4H2O (2), and Na2[Mo2O2S2(R-pdta)]·4H2O (3) have been determined from difTractometer data collected by the use of Mo Kα radiation. The structures of 1, 2, and 3 were refined by the least-squares method to R 0.064, 0.040, and 0.058 for 1370, 2794, and 2141 nonzero reflections respectively. Each Mov ion has a distorted octahedral coordination, and the two coordination octahedra share a common edge to form a binuclear complex. Two terminal oxo ligands are cis to the bridging oxide or sulfide. The R-pdta4− ligand bridges two Mov ions, yielding a Mo–N–CH2–CH(CH3)–N–Mo ring with an equatorial methyl group, the N and carboxyl O atoms occupying the axial (trans to the terminal O) and equatorial positions respectively. A specific distortion of the donor-atom disposition is observed, which is represented as the twist (Δ) of the terminal O–O edges in the (Remark: Graphics omitted.) portion about the axis passing through the mid-points of the O–O edges (Δ denotes the absolute disposition of two skew edges or bonds), and as the twist (Δ) of Mo–N bonds about the Mo–Mo axis. The O=Mo bonds of the O=Mo–Mo=O segment in 1 twist in Δ, but those in 2 and 3 are virtually parallel. The distortion of donor-atom disposition is discussed on the basis of the strain due to chelate-ring formation.

Surface and bulk reduction of bismuth/molybdenum oxides studied by electron spin resonance spectroscopy

E.s.r. spectra due to MoV ions in Bi/Mo mixed oxides reduced under vacuum and by propene show bulk and surface reduction governed by the oxygen diffusion. The equilibrium between the two types of reduction depends on the temperature and the catalyst composition and is independent of the actual reduction process. The e.s.r. spectrum due to surface MoV ions is broadened by dipolar interactions with adsorbed oxygen. The residual spectrum is attributed to sites in which MoV ions are probably associated with lattice defects.