Search

It is necessary to develop an efficient hydrogen evolution catalyst to improve the efficiency of the hydrogen evolution reaction (HER). Herein, a MoS 2 nanosheet is decorated on the Pt-doping biomass yeast cells (MoS 2 @Pt/YC) via a simple hydrothermal process. Reducing the noble metal loading without compromising its performance is a challenging task. The smooth surface of YCs is conducive to the growth of MoS 2 nanosheets, and its functional groups provide attachment sites for metal Pt. The Pt/YC is covered with MoS 2 nanosheets, thus improving the exposed active sites for HER. The obtained MoS 2 @Pt/YC delivers a competitive overpotential of 118 mV at the benchmark current density of 10 mA cm -2 and achieves a small Tafel slope of 74 mV dec -1 , indicating the great HER performance of MoS 2 @Pt/YC. Moreover, MoS 2 @Pt/YC shows robust stability after 24 h of continuous operation toward HER in acidic solution. By introducing transition metal sulfides with high specific surface area, the loading of precious metals can be reduced without compromising properties. This work provides a method to design Pt-doping HER electrocatalysts through a simple method. The facile preparation process for MoS 2 @Pt/YC and its outstanding performance allow it to be a promising electrocatalyst for practical HER application.

A bimetallic molybdenum complex bridged by an activated dinitrogen ligand and supported by phosphine and terpyridine ligands, [{(PhTpy)(PPh2Me)2Mo}2(μ2-N2)][BArF24]2 [PhTpy = 4'-Ph-2,2',6',2"-terpyridine; ArF24 = (C6H3-3,5-(CF3)2)4], was synthesized and structurally characterized, and its electronic structure was determined using a combination of experimental and density functional theory computational methods. Each molybdenum atom is best described as molybdenum(II) bridged by a modestly activated [N2]2- ligand. The cyclic voltammogram of [{(PhTpy)(PPh2Me)2Mo}2(μ2-N2)]2+ displays two reversible reductive and two reversible oxidative features, prompting the preparation and characterization of a series of molybdenum dinitrogen compounds spanning five oxidation states ([{(PhTpy)(PPh2Me)2Mo}2(μ2-N2)][BArF24]n, where n = 4, 3, 2, 1, 0). Raman and 15N NMR spectroscopic data establish that the bridging nitrogen ligand remains intact across the redox series. Electron paramagnetic resonance spectroscopy was used to probe the nature of the unpaired electron in the mixed-valent electronic oxidized and reduced products. The singly occupied molecular orbital is principally metal-based in [{(PhTpy)(PPh2Me)2Mo}2(μ2-N2)]3+ and ligand-localized in [{(PhTpy)(PPh2Me)2Mo}2(μ2-N2)]+. [ABSTRACT FROM AUTHOR]

Newly synthesized octahedral molybdenum cluster compound (n-Bu4N)2[Mo6I8(OOC-1-adamantane)6] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O2(¹Δg). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV-vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O2(¹Δg) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV-vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O2(¹Δg) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O2(¹Δg). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy. [ABSTRACT FROM AUTHOR]

Interligand charge transfer is examined in the novel metallo-dithiolene complex MoO(SPh)2(iPr2Dt0) (where iPr2Dt0 = N,N′-isopropyl-piperazine-2,3-dithione). The title complex displays a remarkable 70° "envelope"-type fold of the five-membered dithiolene ring, which is bent upward toward the terminal oxo ligand. A combination of electronic absorption and resonance Raman spectroscopies have been used to probe the basic electronic structure responsible for the large fold-angle distortion. The intense charge transfer transition observed at ∼18 000 cm-1 is assigned as a thiolate → dithione ligand-to-ligand charge transfer (LL′CT) transition that also possesses Mo(IV) → dithione charge transfer character. Strong orbital mixing between occupied and virtual orbitals with Mo(x²-y²) orbital character is derived from a strong pseudo Jahn-Teller effect, which drives the large fold-angle distortion to yield a double-well potential in the electronic ground state. [ABSTRACT FROM AUTHOR]

Preparation of molybdenum dioxido complexes with novel iminophenolate ligands bearing pendant secondary amide functionalities led to unprecedented C-C and C-N coupling reactions of two α-iminoamides upon coordination. The diastereoselective cyclization to asymmetric imidazolidines occurs at the metal center in two consecutive steps via a monocoupled intermediate. A meaningful mechanism is proposed on the basis of full characterization of intermediate and final molybdenum-containing products by spectroscopic means and by single-crystal X-ray diffraction analyses. This process constitutes the first example of a diastereoselective self-cyclization of two α-iminoamides. [ABSTRACT FROM AUTHOR]

119Sn Mössbauer isomer shift (IS) and quadrupole splitting (ΔEQ) for MSnR bonding in metal-stannylidyne complexes trans-[Cl(PMe3)4MoSn-R] (1), trans-[Cl(PMe3)4WSn-R] (2), trans-[Cl(dppe)2MoSn-R] (3), trans-[Cl(dppe)2WSn-R] (4), [(dppe)2MoSn-R]+ (5), [(dppe)2WSn-R]+ (6) (R = C6H3-2,6-Mes2) have been investigated for the first time. Calculations of optimized structures and 119Sn Mössbauer parameters were carried out at the DFT/TPSS-D3(BJ)/TZVPP/ZORA level of theory. The calculated geometry parameters of stannylidyne complexes of molybdenum and tungsten (1-6) are in good agreement with experimental values of W-Sn and Sn-C bond distances. The calculated values of the isomer shift for the complexes (1-6) are almost same to the experimental values (within ±0.1 mm/s). Experimental values (ISexptl, 2.38-2.50 mm/s) and calculated values (IScalcd, 2.37-2.49 mm/s) of isomer shifts indicate that the oxidation state of tin in the studied complexes with MSn-R bonding is Sn(II). The variations of ISexptl, as a function of Sn s electrons (Ns(Sn)), also exhibit a linear trend. (IS = 0.477Ns(Sn) - 1.888, R² = 0.9973). Calculated values of isomer shift (IScalcd) using the linear regression with the Ns(Sn) electron density are in excellent concord with the ISexptl.The calculated values of nuclear quadrupole splitting parameters (ΔEQ(calcd)) of 119Sn using the relation ΔEQ(calcd) = (0.540 + 0.28) V are in agreement with the experimental values. [ABSTRACT FROM AUTHOR]

Well-defined molecular catalysts for the reduction of N2 to NH3 with protons and electrons remain very rare despite decades of interest and are currently limited to systems featuring molybdenum or iron. This report details the synthesis of a molecular cobalt complex that generates superstoichiometric yields of NH3 (>200% NH3 per Co–N2 precursor) via the direct reduction of N2 with protons and electrons. While the NH3 yields reported herein are modest by comparison to those of previously described iron and molybdenum systems, they intimate that other metals are likely to be viable as molecular N2 reduction catalysts. Additionally, a comparison of the featured tris(phosphine)borane Co–N2 complex with structurally related Co–N2 and Fe–N2 species shows how remarkably sensitive the N2 reduction performance of potential precatalysts is. These studies enable consideration of the structural and electronic effects that are likely relevant to N2 conversion activity, including the π basicity, charge state, and geometric flexibility. [ABSTRACT FROM AUTHOR]

This paper describes our recent progress in catalytic nitrogen fixation by using transition-metal–dinitrogen complexes as catalysts. Two reaction systems for the catalytic transformation of molecular dinitrogen into ammonia and its equivalent such as silylamine under ambient reaction conditions have been achieved by the molybdenum–, iron–, and cobalt–dinitrogen complexes as catalysts. Many new findings presented here may provide new access to the development of economical nitrogen fixation in place of the Haber–Bosch process. [ABSTRACT FROM AUTHOR]

A large family of bifunctional 1,2,4-triazole molecular tectons (tr) has been explored for engineering molybdenum(VI) oxide hybrid solids. Specifically, tr ligands bearing auxiliary basic or acidic groups were of the type amine, pyrazole, 1H-tetrazole, and 1,2,4-triazole. The organically templated molybdenum(VI) oxide solids with the general compositions [MoO3(tr)], [Mo2O6(tr)], and [Mo2O6(tr)(H2O)2] were prepared under mild hydrothermal conditions or by refluxing in water. Their crystal structures consist of zigzag chains, ribbons, or helixes of alternating cis-{MoO4N2} or {MoO5N} polyhedra stapled by short [N-N]-tr bridges that for bitriazole ligands convert the motifs into 2D or 3D frameworks. The high thermal (235-350 °C) and chemical stability observed for the materials makes them promising for catalytic applications. The molybdenum(VI) oxide hybrids were successfully explored as versatile oxidation catalysts with tert-butyl hydroperoxide (TBHP) or aqueous H2O2 as an oxygen source, at 70 °C. Catalytic performances were influenced by the different acidic-basic properties and steric hindrances of coordinating organic ligands as well as the structural dimensionality of the hybrid. [ABSTRACT FROM AUTHOR]

The conserved pterin dithiolene ligand that coordinates molybdenum (Mo) in the cofactor (Moco) of mononuclear Mo enzymes can exist in both a tricyclic pyranopterin dithiolene form and as a bicyclic pterin-dithiolene form as observed in protein crystal structures of several bacterial molybdoenzymes. Interconversion between the tricyclic and bicyclic forms via pyran scission and cyclization has been hypothesized to play a role in the catalytic mechanism of Moco. Therefore, understanding the interconversion between the tricyclic and bicyclic forms, a type of ring-chain tautomerism, is an important aspect of study to understand its role in catalysis. In this study, equilibrium constants (Keq) as well as enthalpy, entropy, and free energy values are obtained for pyran ring tautomerism exhibited by two Moco model complexes, namely, (Et4N)[Tp*Mo(O)(S2BMOPP)] (1) and (Et4N)[Tp*Mo(O)(S2PEOPP)] (2), as a solvent-dependent equilibrium process. Keq values obtained from ¹H NMR data in seven deuterated solvents show a correlation between solvent polarity and tautomer form, where solvents with higher polarity parameters favor the pyran form. [ABSTRACT FROM AUTHOR]

The phosphinidene-bridged complexes [Mo2Cp2(μ-κ¹:κ¹,η6-PR*)(CO)2] (1), [Mo2Cp2(μ-κ¹:κ¹,η4-PR*)(CO)3] (2), [Mo2Cp(μ-κ¹:κ¹,η5-PC5H4)(η6-HR*)(CO)2] (3), and [Mo2Cp2(μ-κ¹:κ¹-PH)(η6-HR*)(CO) 2] (4) were examined as precursors of heterometallic gold(I) and related derivatives (Cp = η5-C5H5, R* = 2,4,6-C6H2tBu3). These complexes reacted with [AuCl(THT)] to give the corresponding derivatives [AuMo2ClCp2(μ-κ¹:κ¹:κ¹,η6-PR*)(CO)2], [AuMo2ClCp2(μ-κ¹:κ¹:κ¹,η4-PR*)(CO)3] (Au-Mo = 2.8493(6) Å), [AuMo2ClCp(μ-κ¹:κ¹:κ¹,η5-PC5H4)(CO)2 (η6-HR*)], and [AuMo2ClCp2(μ3-PH)(CO)2(η6-HR*)] formally resulting from the addition of an acceptor AuCl moiety to the short Mo-P bond of the parent substrates almost perpendicular to the corresponding Mo2P plane. The chloride ligand was easily displaced upon reaction of the PC5H4-bridged gold complex with K[MoCp(CO)3] to give the tetranuclear derivative [AuMo3Cp2(μ-κ¹:κ¹:κ¹,η5-PC5H4)(CO)5(η6-HR*)] (Au-Mo = 2.711(2) and 2.807(2) Å). Compound 1 also reacted with HgI2 to give a hexanuclear complex [HgMo2Cp2(μ-I)I(μ-κ¹:κ¹,η6-PR*)(CO) 2]2 containing dative Mo→Hg bonds (2.820(1) and 2.827(1) Å), whereas complex 3 gave the μ3-PR bridged complex [HgMo2CpI2(μ-κ¹:κ¹:κ¹,η5-PC5H4)(CO)2(η6-HR*)]. Complexes 1 to 4 also reacted easily with [AuL(THT)]PF6(L = THT, P(p-tol)3, PMe3, PiPr3) to give the corresponding cationic trinuclear derivatives [AuMo2Cp2(μ-κ¹:κ¹:κ¹,η6-PR*)(CO) 2L](PF6) (Au-Mo = 2.8080(3) Å for L = P(p-tol)3), [AuMo2Cp2(μ-κ¹:κ¹:κ¹,η4-PR*)(CO)3L](PF6), and [AuMo2Cp(μ-κ¹:κ¹:κ¹,η5-PC5H4)(CO)2(η6-HR*){P(p-tol)3}](PF6). The blue, analogous PH-bridged complexes were more conveniently isolated as tetra-arylborate salts [AuMo2Cp2(μ3-PH)(CO)2(η6-HR*)L](BAr'4) (Au-Mo = 2.8038(6) Å for L = PiPr3; Ar'= 3,5-C6H3(CF3)2]. Compounds 1, 3, and 4 reacted readily with the cation [Au(THT) 2]+ (as PF6- or BAr'4- salts) in a 2:1 ratio to give respectively the corresponding pentanuclear derivatives [Au{Mo2Cp2(μ-κ¹:κ¹:κ¹,η6-PR*)(CO) 2}2](PF6), [Au{Mo2Cp(μ-κ¹:κ¹:κ¹,η5-PC5H4)(CO)2(η6-HR*)}2](PF6) (Au-Mo = 2.7975(7) and 2.8006(7) Å), and [Au{Mo2Cp2(μ3-PH)(CO)2(η6-HR*)}2](BAr'4) (Au-Mo = 2.8233(8) and 2.8691(7) Å). Related silver complexes were obtained from the reaction of 3 and 4 with [AgCl(PPh3)]4 after spontaneous symmetrization, while reaction of 1 with [Cu(NCMe)4]PF6 in a 2:1 ratio yielded the analogous copper complex [Cu{Mo2Cp2(μ-κ¹:κ¹:κ¹,η6-PR*)(CO) 2}2](PF6). All the above cationic gold complexes having (μ-κ¹:κ¹:κ¹,η6-PR*) ligands (but not the copper complex) rearranged into [Au{Mo2Cp(μ-κ¹:κ¹:κ¹,η5-PC5H4)(CO)2(η6-HR*)}2](PF6) in refluxing 1,2-dichloroethane solution. [ABSTRACT FROM AUTHOR]

Maximizing the usable space of electrocatalysts and fine-tuning the interface geometry as well as the electronic structure to facilitate hydrogen and oxygen evolution reactions (HER and OER) have always been the focus of research. Herein, a homogeneous porous nanoparticle construction strategy was proposed, in which molybdenum nitride (Mo 2 N) particles were prepared by controlled heat treatment of the precursor nanoparticle induced by polyethylene glycol, and the Mo 2 N/Co-C 3 N 4 heterostructure with a pore size of about 1.13 nm was obtained by compounding Co-anchored graphitic carbon nitride. In particular, exploring the change of charge distribution at the interface based on the principle of "electron complementation" shows that under the regulation of nitrogen with high electronegativity, the affinity of active site Co to oxygenated species in the OER process and the adsorption as well as cleavage ability of HER reactants in the active site were effectively optimized. Thus, Mo 2 N/Co-C 3 N 4 not only inherits the functions of each component, but also provides an ideal heterogeneous interface for exhibiting impressive bifunctional activity, which only needs 100 and 210 mV to deliver 10 mA cm -2 for the HER and OER, respectively. In addition, the Mo 2 N/Co-C 3 N 4 catalyst also demonstrates high overall water splitting stability with a slight current decrease after 95 h. Manipulating the electronic structure of multiple sites by constructing electronically complementary interfaces may provide another avenue to develop highly active catalysts for overall water splitting and other applications.

Homogeneous light-driven systems employing molecular molybdenum catalysts for hydrogen production are described. The specific Mo complexes studied are six-coordinate bis(benzenedithiolate) derivatives having two additional isocyanide or phosphine ligands to complete the coordination sphere. Each of the complexes possesses a trigonal prismatic coordination geometry. The complexes were investigated as proton reduction catalysts in the presence of [Ru(bpy)3]2+, ascorbic acid, and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis occurs between the MoIV/MoIII and MoIII/MoII redox couples, around 1.0 V vs SCE. Mechanistic studies by ¹H NMR spectroscopy show that upon two-electron reduction the Mo(CNR)2(bdt)2 complex dissociates the isocyanide ligands, followed by addition of acid to result in the formation of molecular hydrogen and the Mo(bdt)2 complex. [ABSTRACT FROM AUTHOR]

A series of La3BW1-xMoxO9:Eu3+ (x = 0-0.4) polycrystalline powders were prepared by using solid-state reactions. The phase structure, UV-vis absorption spectra, and photoluminescence properties were studied as a function of the Mo/W ratio. When Mo6+ ions are incorporated into the lattice, the characteristic sharp lines in the excitation spectra of Eu3+ monitored at 617 nm are prominently enhanced, which join the ligand-to-metal charge transfer (LMCT) band of La3BW1-xMoxO9:Eu3+ into a broad band ranging from 250 to 450 nm centered at 375 nm. The intensity of the broad excitation band reaches a maximum when the content of Mo6+ ions increases to x = 0.3. On the other hand, the LMCT band around 306 nm decreases and shifts toward the longer wavelength. These features are advantageous to near-UV or blue light GaN-based LED applications. Orbital population analysis by density functional theory calculation (DFT) reveals that the near-UV excitation of La3BW1-xMoxO9:Eu3+ red phosphor is due to the electronic transition from the O 2p orbital to the W 5d and Mo 4d orbitals, respectively. With the introduction of Mo6+ into the lattice, the band gap of La3BW1-xMoxO9 becomes narrower than that of the pure phase La3BWO9. [ABSTRACT FROM AUTHOR]

Attempts to prepare low-valent molybdenum complexes that feature a pentadentate 2,6-bis(imino)pyridine (or pyridine diimine, PDI) chelate allowed for the isolation of two different products. Refluxing Mo(CO)6 with the pyridinesubstituted PDI ligand, PyEtPDI, resulted in carbonyl ligand substitution and formation of the respective bis (ligand) j compound (PyEtPDl2Mo (l). This complex was investigated by single-crystal X-ray diffraction, and density functional theory calculations indicated that 1 possesses a Mo(0) center that back-bonds into the π*-orbitals of the unreduced PDI ligands. Heating an equimolar solution of Mo(CO)6 and the phosphine-substituted PDI ligand, Ph2PPrPDI, to 120°C allowed for the preparation of (ph2PPrPDI)Mo(CO)(2), which is supported by a K5-N,N,N,P,P-1,ph2PPrPDl chelate. Notably, 1 and 2 have been found to catalyze the hydrosilylation of benzaldehyde at 90°C, and the optimization of 2-catalyzed aldehyde hydrosilylation at this temperature afforded turnover frequencies of up to 330 h-1. Considering additional experimental observations, the potential mechanism of 2-mediated carbonyl hydrosilylation is discussed. [ABSTRACT FROM AUTHOR]

A series of terephthalate-bridged dimolybdenum dimers with various formamidinate ancillary hgands, denoted as [Mo2(ArNCHNAr)3]2μ-O2CC6H4CO2) (Ar=p-XC6H4, with X = OCH3 (1), CH3 (2), F (3), Cl (4), OCF, (5), and CF3 (6)), has been synthesized and studied in terms of substituent effects on electron delocalization between the two dimetal sites. X-ray structural analyses show that these complexes share the same molecular scaffold with the para-substituents (X) being about 8 A away from the Mo2 center. It is found that the remote substituents have the capability to tune the electronic properties of the complexes. For the series 1 to 6, the metal--metal bond distances (dMo_Mo) decrease slightly and continuously; the potential separations (ΔE1/2) for the two successive one-electron oxidations decrease constantly, and the metal to ligand transition energies (&#955max) increase in order. More interestingly, the two types of methine protons, H∥ on the horizontal and H⊥ on the vertical ligands with respect to die plane defined by the Mo--Mo bond vectors and bridging ligand, display separate resonant signals δ∥ and δ⊥ in the NMR spectra. The displacements of the chemical shifts, Δ&#948∥-⊥ = &#948∥ are getting smaller as the substituents vary from electron-donating to -withdrawing. These results show that the peripheral groups on the [Mo2] units function to fine-tune the metal--metal interactions crossing the bridging ligand. The experimental parameters, ΔE1/2, &#955max and Δ&#948∥-⊥ which are linearly related with the Hammett constants (σx) of the X groups, can be used to probe the charge density on the two [Mo2] units and the electronic delocalization between them. [ABSTRACT FROM AUTHOR]

The crystal structures, phase transition, and thermal expansion behaviors of solid solutions of Sc2-aFexMo3O12 (0 ≤ x ≤ 2) have been examined using X-ray diffraction (XRD), neutron powder diffraction (NPD), and differential scanning calorimetry (DSC). At room temperature, samples crystallize in a single orthorhombic structure for the compositions of x < 0.6 and monoclinic for x > 0.6, respectively. DSC results indicate that the phase transition temperature from monoclinic to orthorhombic structure is enhanced by increasing the Fe3* content. Hightemperature XRD and NPD results show that Sc1.3Fe0.7Mo3O12 exhibits near zero thermal expansion, and the volumetric coefficients of thermal expansion derived from XRD and NPD are 0.28 X 10-6°C-1 (250-80 0°C) and 0.65 X 10-6°C-1 (227-427°C), respectively. NPD results of Sc2Mo3O12 (x = 0) and Sc1.3Fe0.7Mo3O12 (x = 0.7) indicate that Fe substitution for Sc induces reduction of the mean Sc(Fe)--Mo nonbond distance and the different thermal variations of Sc(Fe)--O5--Mo2 and Sc(Fe)--O3--Mo2 bond angles. The correlation between the displacements of oxygen atoms and the variation of unit cell parameters was investigated in detail for Sc2Mo3012. [ABSTRACT FROM AUTHOR]

The six-coordinate molybdenum{IV) oxido isocya nide complex 1 [?,?-OC-6-2-3-[MoO(NPnNi)(CNtBu)]; NpnNi = 4-tert-butylphenyl(pyrrolato-2-ylmethylene)amine] is obtained in diastereomerically pure form in the solid state, as revealed by single-crystal X-ray diffraction. In solution, this stereoisomer equilibrates with the ?,?-OC-6-2-4 diastereomer 2 at ambient temperature. The stereochemistry of both isomers has been elucidated by NMR, IR, and UV/vis spectroscopy in combination with density functional theory (DFT)/polarizable continuum model and time-dependent DFT calculations. The isomerization 1 -- 2 is suggested to proceed via a dissociative trigonal twist with dissociation of the imine nitrogen donor Ni of one chelate ligand (hemilabile ligand) rather than dissociation of the monodentate isocyanide ligand. The isomerization barrier has been experimentally determined as 91 and 95 kJ mol-1 in tetrahydrofuran and toluene, respectively. [ABSTRACT FROM AUTHOR]

Molybdenum enzymes contain at least one pyranopterin dithiolate (molybd op terin, MPT) moiety that coordinates Mo through two dithiolate (dithiolene) sulfur atoms. For sulfite oxidase (SO), hyperfine interactions (hfi) and nuclear quadrupole interactions (nqi) of magnetic nuclei (I ? 0) near the Mo(V) (d¹) center have been measured using high-resolution pulsed electron paramagnetic resonance (EPR) methods and interpreted with the help of density functional theory (DFT) calculations. These have provided important insights about the active site structure and the reaction mechanism of the enzyme. However, it has not been possible to use EPR to probe the dithiolene sulfurs directly since naturally abundant 32S has no nuclear spin (I = 0). Here we describe direct incorporation of 33S (I = 3/2), the only stable magnetic sulfur isotope, into MPT using controlled in vitro synthesis with purified proteins. The electron spin echo envelope modulation (ESEEM) spectra from 33S-labeled MPT in this catalytically active SO variant are dominated by the "interdoublet" transition arising from the strong nuclear quadrupole interaction, as also occurs for the 33S-labeled exchangeable equatorial sulfite ligand [Klein, E. L., et al. Inorg. Chem. 2012, 51, 1408-1418]. The estimated experimental hfi and nqi parameters for 33S (aiso = 3 MHz and e²Qq/h = 25 MHz) are in good agreement with those predicted by DFT. In addition, the DFT calculations show that the two 33S atoms are indistinguishable by EPR and reveal a strong intermixing between their out-of-plane p2 orbitals and the dxy orbital of Mo(V). [ABSTRACT FROM AUTHOR]

A series of pseudosymmetrical structures of formula K10(M2OnF11-n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2>; M = Mo, n = 4, X = CI, Br4/2, I4/2) illustrates generation of polar structures with the use of A- shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d° early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn--Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11_n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3ml or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or A-shaped bimetallic BBUs and related packing effects. These A-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs. [ABSTRACT FROM AUTHOR]

Coordination compounds oxido(diperoxido)(S-butyl-N-methyl-S-(2-pyridyl)sulfoximine)molybdenum(VI), [MoO(O2)2{SO(NMe)nBu(NC5H4)}] (5c), and bis{(dichlorido)(N,S-dimethyl-2-pyridylsulfoximine)iron(II)}, tetrahydrofuran solvate (1:1) (6), [FeCl2{SO(NMe)Me(NC5H4)}]2·THF are prepared from the free ligand 4 and molybdenum(VI) oxidediperoxide(dihydrate) and iron dichloride, respectively. The crystal structures reveal a trigonal bipyramid with the pyridine ring and the single oxygen on molybdenum in a trans arrangement for 5c and a planar π²-Cl2Fe2 ring with trans-oriented exocyclic Cl atoms for 6 whereas the structures of the N,N-dicoordinated ligands are only little effected by the metals. Coordination compounds (5) efficiently catalyze the epoxidation of cyclooctene or of monosubstituted alkenes by tert-butyl hydroperoxide. [ABSTRACT FROM AUTHOR]

In the solid tate, tris(3,5-di-tert-butylcatecholato)molybdenum(VI) forms a dimer with seven-coordinate molybdenum and bridging catecholates. NMR spectroscopy indicates that the dimeric structure is retained in solution. The molybdenum center has a high affinity for Lewis bases such as pyridine or pyridine-N-oxide, forming seven-coordinate monomers with a capped octahedral geometry, as illustrated by the solid-state structure of (3,5-tBu2Cat)3Mo(py). Structural data indicate that the complexes are best considered as Mo(VI) with substantial p donation from the nonbridging catecholates to molybdenum. Both the dimeric and the monomeric tris(catecholates) react rapidly with water to form free catechol and oxomolybdenum bis(catecholate) complexes. Monooxomolybdenum complexes are also obtained, more slowly, on reaction with dioxygen, with organic products consisting mostly of 3,5-di-tert-butyl-1,2-benzoquinone with minor amounts of the extradiol oxidation product 4,6-di-tert-butyl-1-oxacyclohepta-4,6-diene-2,3-dione. The pyridine-N-oxide complex reacts on heating (with excess pyO) to form initially (3,5-tBu2Cat)2MoO(Opy) and ultimately MoO3(Opy), with quinone and free pyridine as the only organic products. The decay of (3,5-tBu2Cat)3Mo(Opy) shows an accelerated, autocatalytic profile because the oxidation of its product, (3,5-tBu2Cat)2MoO(Opy), produces an oxo-rich, catecholate-poor intermediate which rapidly conproportionates with (3,5-tBu2Cat)3Mo(Opy), providing an additional pathway for its conversion to the mono-oxo product. The tris(catecholate) fragment Mo(3,5-tBu2Cat)3 deoxygenates Opy in this nonclassical oxygen atom transfer reaction slightly less rapidly than does its oxidized product, MoO(3,5-tBu2Cat)2. [ABSTRACT FROM AUTHOR]

Three novel dimolybdenum dimers [Mo2(DAniF)3]2(μ-OSCC6H4CSO), [Mo2(DAniF)3]2(μ-o2CC6H4CS2), and [Mo2(DAniF)3]2(μ-S2CC6H4CS2) (DAniF = N,N'-di(p-anisyl)formamidinate) have been synthesized and characterized by single-crystal X-ray diffractions. Together with the terephthalate analogue, the four compounds, denoted as [o2-o2]+, [OS-OS]+, [S2-S2], and [o2-S2], have similar molecular skeletons and Mo2···Mo2 separations (12 Å), but varying sulfur contents or symmetry. The singly oxidized complexes [o2-o2]+, [OS-OS]+, [S2-S2]+, and [o2-S2]+ display characteristic intervalence transition absorption bands in the near- and mid-IR regions, with differing band energy, intensity, and shape. Applying the geometrical length of the bridging group "-CC6H4C-" (5.8 Å) as the effective electron transfer distance, calculations from the Mulliken-Hush equation yield electronic coupling matrix elements (Hab) in the range 600-900 cm-1. Significantly, this series presents a transition from electron localization to "almost-delocalization" as the carboxylate groups of the bridging ligand are successively thiolated. In terms of Robin-Day's scheme, [S2-S2]+M is best described as an intermediate between Class II and III, while [o2-o2]+ and [OS-OS]+ belong to Class II. It is unusual that the Class II-III transition occurs in such a weakly coupled system (Hab < 1000 cm-1). This is attributed to the d(d)-p(p) conjugation between the Mo2+ center and bridging ligand. By electrochemical and spectroscopic methods, the internal energy difference for [o2-S2]+ is determined to be 2250 ± 80 cm-1, which controls the charge distribution of the cation radical. The experimental results and theoretical analyses illustrate that the unsymmetrical geometry leads to unbalanced electronic configurations and asymmetrical redox and optical behaviors. [ABSTRACT FROM AUTHOR]

Exploring effective sensors for detecting possible hazards in a water system are greatly significant. This work proposed a strategy for stable and effective bifunctional sensors via incorporating hourglass-type phosphomolybdates into metal-organic fragments to construct a high-dimensional framework. Two hourglass-type phosphomolybdate-based electrochemical sensors toward heavy metal ion Cr(VI) and tetracycline (TC) detection were designed with the formula [Co II 2 (H 2 O) 4 Na I 2 ][Co II (Hbpe)][Na I (bpe) 1.5 ]{Co II [P V 4 Mo V 6 O 31 H 6 ] 2 }·9H 2 O ( 1 ) and [Co II (H 2 O) 4 Na I 3 ][Co II (Hbpe)][Co II (bpe)]{Co II [P V 4 Mo V 6 O 31 H 6 ] 2 }·9H 2 O ( 2 ) [bpe = 1,2-di(4-pyridyl)ethylene]. Structural analysis showed that hybrids 1 and 2 possess three-dimensional POM-supported network features with favorable stability and exhibit reversible redox properties. Experiments found that this kind of hybrids as efficient sensors have excellent electrochemical performance toward Cr(VI) detection with high sensitivities of 0.111 μA·μM -1 for 1 and 0.141 μA·μM -1 for 2 , fast response time of 1 s, and low detection limits of 30 nM for 1 and 27 nM for 2 , which far meet the standard of WHO for drinking water. Moreover, hybrids 1-2 also exhibit fast responses to TC detection with sensitivities of 0.0073 and 0.022 μA·mM -1 and detection limits of 0.426 and 0.084 mM. This work offers a novel strategy for the purposeful design of efficient POM-based electrochemical sensors for accurate determination of contaminants in a practical water system.

Molybdenum dinitrogen complexes are presented which are supported by novel hybrid tripod ligands of the type Me-C(CH2PPh2)2(CH2PiPr2) (trpd-1) and H-C(CH2PPh2)(CH2PiPr2)2 (trpd-2) having mixed dialkylphosphine/diarylphosphine donor groups. Reaction of the ligand trpd-1with [MoI3(thf)3] followed by sodium amalgam reduction in the presence of the dppm gives the dinitrogen complex [Mo(N2)(trpd-1)(dmpm)] where trpd-1 is coordinated in a ?3 fashion. The complex exhibits a moderate activation of N2 which enables its protonation under retention of the pentaphosphine ligation. Replacement of dmpm by the sterically more demanding coligand dppm is found to hamper coordination of N2 and leads to [Mo(trpd-1)(dppm)], the first structurally characterized five-coordinate Mo(0) complex with a phosphine-only ligand sphere. Employing the ligand trpd-2 along with the diphosphines dmpm and dppm in an analogous synthetic route results in a mixture of the bis(dinitrogen) complexes trans-[Mo(N2)2(?2-trpd-2)(diphosphine)] and trans-[Mo(N2)2(iso-?2-trpd-2)(diphosphine)] where the tripod ligand trpd-2 coordinates with two phosphine arms and one phosphine group (PPh2 or PiPr2, respectively) is free. Similar results are obtained with the pure alkyl- and arylphosphine tripod ligands H-C(CH2PiPr2)3 (trpd-3) and H-C(CH2PPh2)3 (tdppmm), leading to trans-[Mo(N2)2(?2-trpd-3)(diphos)] and trans-[Mo(N2)2(?2-tdppmm)(dmpm)], respectively. The electronic and steric reasons for the experimental findings are considered, and the implications of the results for the area of synthetic nitrogen fixation with molybdenum phosphine systems are discussed. [ABSTRACT FROM AUTHOR]

Using new 'normal'-substituted 1,2,3-triazolylidene silver compounds as starting materials allowed for preparation of a series of molybdenum, ruthenium, rhodium, and palladium transition metal complexes bound to the new 1,2,3-triazolylidene ligand system. In this work, the first triazolylidene Mo compound is presented as well as the first structural investigation of a silver complex with a monodentate 1,2,3-triazolylidene. Furthermore, the triazolylidene Pd complex and the Mo complex were tested as precatalysts in Suzuki-Miyaura coupling and epoxidation catalysis, respectively. [ABSTRACT FROM AUTHOR]

The syntheses, crystallographic structures, magnetic properties, and theoretical studies of two heptacoordinated molybdenum complexes with N,N'-bis (3,5-di-tert-butyl-2-hydroxy-phenyl)-l,2-phenylenediamine (H4N2O2) are reported. A formally molybdenum(Vl) complex [Mo(N2O2)CI2(dmf)2] (l) was synthesized by the reaction between [MoO2Cl2(dmf)2] and H4N2O2, whereas the other molybdenum(VI) complex [Mo(N2O2)(HN2O2)] (2) was formed when [MoO2(acac)2] was used as a molybdenum source. Both complexes represent a rare case of the MoVIion without any multiply bonded terminal ligands. In addition, molecular structures, magnetic measurements, ESR spectroscopy, and density functional theory calculations indicate that complex 2 is the first stable molybdenum (VI) amidophenoxide radical. [ABSTRACT FROM AUTHOR]

Five dinitrogen--molybdenum complexes bearing bis-(diphenylphosphino)amine derivative ligands (LR) that form a unique 4-membered P-N-P chelate ring, írans-[Mo(N2)2(LR)2 (2R: R = Ph, Xy, p-MeOPh, 3,5-iPr2Ph,iPr), were prepared for the purpose of binding a dinitrogen molecule. The corresponding two dichloride-molybdenum complexes, trans-[MoCl2(LR)2] (lR: R = Ph, Xy), were also prepared as comparisons. FT-IR spectra of 2R were measured and compared the v(N≡N) values. Moreover, X-ray crystal structure determination of 1R (R = Ph, X) and 2R (R = Xy, 3,5-iPr2Ph) is performed. These experimental results indicated that the coordinated dinitrogen molecule gets easily influenced by the N-substitutent of diphosphinoamine ligand. In addition, to investigate the effect of the properties of the diphosphinoamine ligand for the dinitrogen molybdenum complexes, we performed DFT calculations that focused on the difference of N-substituent, the dihedral angle between P-N-P plane and N-substituent aryl group, and the P--N--P bite angle. This calculation revealed that the competition between the back-donation from metal to dinitrogen and that from metal to ligand was affected by P--N--P bite angle and the dihedral angle of N-substituent of ligand. In order to examine the reactivity with respect to conversion of dinitrogen to ammonia, protonation and trimethylsilylation reactions of the coordinated dinitrogens were carried out for 2R. [ABSTRACT FROM AUTHOR]

Thermolysis of an in situ generated intermediate, produced from the reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) and [LiBH4.THF], with excess Te powder yielded isomeric [(Cp*Mo)2B4TeH5Cl] (2 and 3), [(Cp*Mo)2B4(μ3-OEt)TeH3Cl] (4), and [(Cp*Mo)4B4H4(μ4-BH)3] (5). Cluster 4 is a notable example of a dimolybdaoxatelluraborane cluster where both oxygen and tellurium are contiguously bound to molybdenum and boron. Cluster 5 represents an unprecedented metal-rich metallaborane cluster with a cubane core. The dimolybdaheteroborane 2 was found to be very reactive toward metal carbonyl compounds, and as a result, mild pyrolysis of 2 with [Fe2(CO)9] yielded distorted cubane cluster [(Cp*Mo)2(BH)4(μ3-Te){Fe(CO)3}] (6) and with [Co2(CO)8] produced the bicapped pentagonal bipyramid [(Cp*MoCo)2B3H2(μ3-Te)(μ-CO){Co3(CO)6}] (7) and pentacapped trigonal prism [(Cp*MoCo)2B3H2(μ3-Te)(μ-CO)4{Co6(CO)8}] (8). The geometry of 8 is an example of a heterometallic boride cluster in which five Co and one Mo atom define a trigonal prismatic framework. The resultant trigonal prism core is in turn capped by two boron, one Te, and one Co atom. In the pentacapped trigonal prism unit of 8, one of the boron atoms is completely encapsulated and bonded to one molybdenum, one boron, and five cobalt atoms. All the new compounds have been characterized in solution by IR, 1H, 11B, and 13C NMR spectroscopy, and the structural types were unambiguously established by crystallographic analysis of 2 and 4-8. [ABSTRACT FROM AUTHOR]

A number of local and integral topological parameters of the electron deiLsity of relevant bonding interactions in the binuclear molybdenum complexes [Mo2Cl8]4-, [Mo2(μ-CH3CO2)4], [Mo2(μ-CH3CO2)4], [Mo2(μ-CH3CO2)4Br2]2-, [Mo2(μ-CF3CO2)4Br2]2-, [Mo2(μ-CH3CO2)2Cl4]2-, [Mo2(μ-CH3CO2)2(&mgr;-Cl)2Cl4]2- and [Mo2(μ-Cl)3Cl6]3- have been calculated and interpreted under the perspective of the quantum theory of atoms in molecules (QTAIM). These data have allowed a comparison between related but different atom--atom interactions, such as different Mo--Mo formal bond orders, ligand-unbridged versus Cl-bridged, CH3C02-bridged, and CF3CO2-bridged Mo--Mo interactions, and Mo--Clterminal and Mo-Clbridge versus Mo--Br and Mo--O interactions. Calculations carried out using nonrelativistic and relativistic approaches afforded similar results. [ABSTRACT FROM AUTHOR]

A new route is developed for the synthesis of molybdenum and tungsten porphyrins using [M(NO)2py2Cl2] (M = Mo, W) as the metal source and TPP (dianion of 5,10,15,20-meso-tetraphenylporphyrin) in the benzoic acid melt. Complexes [MoVO(TPP)(OOCPh)] (1) and [WVO(TPP)(OOCPh)] (2) are isolated in almost quantitative yield. These are characterized by single-crystal X-ray structure analysis, electron paramagnetic resonance, electronic and IR spectroscopy, and magnetic moment measurements. Benzenethiol substitutes for PhCOO- in 1, forming an intermediate thiolato complex that responds to the intramolecular redox reaction across the MoV-SPh bond to yield [MoIVO(TPP)] (3). Under an excess of benzenethiol, PhS- is coordinated to the vacant site in 3, which under aerial oxidation is oxidized to benzenesulfonate to form [MoVO(TPP)(O3SPh)] (4). 2 undergoes similar aerial oxidation chemistry albeit slowly. [ABSTRACT FROM AUTHOR]

The reactions of cis-[MoCl(η3-methallyl)(CO)2(NCMe)2] (methallyl = CH2C(CH3)CH2) with Na(NCNCN) and pz*H (pzH, pyrazole, or dmpzH, 3,5-dimethylpyrazole) lead to cis-[Mo(η3-methallyl)(CO)2(pz*H)- (μ-NCNCN-κ2N,N)]2 (pzH, 1a; dmpzH, 1b), where dicyanamide is coordinated as bridging ligand. Similar reactions with fac-[MnBr- (CO)3(NCMe)2] lead to the pyrazolylamidino complexes fac-[Mn(pz*H)-(CO)3(NH=C(pz*)NCN-κ2N,N)] (pzH, 2a; dmpzH, 2b), resulting from the coupling of pyrazol with one of die CN bonds of dicyanamide. The second CN bond of dicyanamide in 2a undergoes a second coupling with pyrazole after addition of 1 equiv of fac-[MnBr(CO)3(pzH)2], yielding die dinuclear doubly coupled complex [{fac-Mn(pzH)(CO)3}2(μ-NH=C(pz)NC(pz) =NH-κ4N,N,N,N)]Br (3). The crystal structure of 3 reveals the presence of two isomers, eis or trans, depending on whether the terminal pyrazoles are coordinated at die same or at different sides of the approximate plane defined by die bridging bisamidine ligand. Only the eis isomer is detected in die crystal structure of the perchlorate salt of the same bimetallic cation (4), obtained by metathesis with AgClO4. All the N-bound hydrogen atoms of the cations in 3 or 4 are involved in hydrogen bonds. Some of the C-N bonds of the pyrazolylamidino ligand have a character intermediate between single and double, and theoretical studies were carried out on 2a and 3 to confirm its electronic origin and discard packing effects. Calculations also show die essential role of bromide in the planarity oi the tetradentate ligand in die bimetallic complex 3. [ABSTRACT FROM AUTHOR]

The molybdenum(V) complex [Mo(O)Cl3dppe] [dppe = 1,2-bis(diphenylphosphino)ethane] is considered as a model system for a combined study of the electronic structure using UV/vis absorption and magnetic circular dichroism (MCD) spectroscopy. In order to determine the signs and MCD C-term intensities of the chlorido → molybdenum charge-transfer transitions, it is necessary to take the splitting of the excited doublet states into sing-doublet and trip-doublet states into account. While transitions to the sing-doublet states are electric-dipole-allowed, those to the trip-doublet states are electric-dipole-forbidden. As spin-orbit coupling within the manifold of sing-doublet states vanishes, configuration interaction between the sing-doublet and trip-doublet states is required to generate the MCD C-term intensity. The most prominent feature in the MCD spectrum of [Mo(O)Cl3dppe] is a "double pseudo-A term", which consists of two corresponding pseudo-A terms centered at 27000 and 32500 cm-1. These are assigned to the ligand-to-metal charge-transfer transitions from the pp orbitals of the equatorial chlorido ligands to the Mo dyz and dxz orbitals. On the basis of the theoretical expressions developed by Neese and Solomon (Inorg. Chem.1999, 38, 1847-1865), a general treatment of the MCD C-term intensity of these transitions is presented that explicitly considers the multideterminant character of the excited states. The individual MCD signs are determined from the corresponding transition densities derived from the calculated molecular orbitals of the title complex (BP86/LANL2DZ). [ABSTRACT FROM AUTHOR]

Various complexes of the types [Mo(DAD)(CO)3L] (L = CO, MeCN, MeOH, THF, DMSO, DMF, Me2CO, EtOAc, THT, ImH, Im1, tBuNC, nBu3P), (ER4)[Mo(DAD)(CO)3X] (ER4 = NEt4+; X- = Cl-, Br-, I-, NCS-, CN- and ER4+ = PPh4+; X- = N3-), and (ER4)[{Mo(DAD)(CO)3}2(μ-X)] (ER4+ = NEt4+; X- = CN-, OAc- and ER4+ = PPh4+; X- = N3-; DAD = N,N'-bis(2,6-dimethylphenyl)butane-2,3-diimine) were prepared by ligand exchange from cycloheptatriene molybdenum tricarbonyl. A total of 19 crystal structures were determined, including unprecedented structural characterization of molybdenum(0) coordination by dimethyl sulfoxide (DMSO), methanol, ethyl acetate (EtOAc), acetone, and N,N-dimethylformamide (DMF). Correlation of 13C NMR shifts with the complex geometry suggests a direct ligand-ligand interaction between DAD and O-bonded coligands with C=O and S=O double bonds, such as EtOAc, Me2CO, DMF, and DMSO. Unexpectedly, the solvatochromic properties of these tricarbonyl complexes [Mo(DAD)(CO)3L] are unfavorable for the determination of Kamlet-Taft parameters of the corresponding solvent L. Contrastingly, the UV/vis absorption of [Mo(DAD)(CO)4] is strongly correlated with the Kamlet-Taft parameter π*, which is shown for 22 solvents, including seven room temperature ionic liquids. [ABSTRACT FROM AUTHOR]

In the Bi2O3-MO-P2O5 ternary system, the commonly observed sizable ID ribbon-like units have been extended to their 2D infinite end member, leading to the novel tailormade Bi4MO4(PO4)2 compounds. It contains planar [Bi2O2]2+ derivatives, separated by two slabs of PO4, which create channels hosting the M2+ cations (M = Mg, Zn). For both compounds, supercell orderings occur comparatively to the predicted ideal crystal structure (VMg, = 2Videal and VZn = 8Videal). In die Mg case a transition into the ideal lattice occurs above 450 °C. In spite of the conceptual assembly of 2D motifs, the final architecture is three-dimensional due to strong interbonds. Thus, our work gives new insights on the possibility for versatile organization of original secondary building units (SBUs) able to self-assemble into predicted structural edifices. Single-crystal and powder XRD versus temperature, high-temperature 31P NMR, as well as transmission electron microscopy were used for structural characterization. Preliminary electric characterization is also reported. [ABSTRACT FROM AUTHOR]

Reaction coordinates for oxo transfer from the substrates Me5NO, Me2SO, and Me3PO to the biologically relevant Mo(IV) bis-dithiolene complex [Mo(OMe)(mdt)2] where mdt 1,2-dimethyl-ethene-l,2-dithiolate(2-), and from Me2SO to the analogous W(IV) complex, have been calculated using density functional theory. In each case, the reaction first proceeds through a transition state (TS1) to an intermediate with substrate wealdy bound, followed by a second transition state (TS2) around which breaking of the substrate X-O bond begins. By analyzing the energetic contributions to each barrier, it is shown that the nature of the substrate and metal determines which transition state controls the rate-determining step of the reaction. [ABSTRACT FROM AUTHOR]

The site occupancies of the Mo-Ni-Re σ phase have been studied as a function of the composition in the ternary homogeneity domain by both experimental measurements and calculations. Because of the possible simultaneous occupancy of three elements on the five sites of the crystal structure, the experimental determination of the site occupancies was achieved by using combined Rietveld refinement of X-ray and neutron diffraction data, whereas calculation of the site occupancies was carried out by using the density functional theory results of every ordered (i.e., 35 = 243) configuration appearing in the ternary system. A comparison of the experimental and calculation results showed good agreement, which suggests that the topologically close-packed phases, such as the σ phase, could be described by the Bragg-Williams approximation (i.e., ignoring the short-range-order contributions). On the other hand, the atomic distribution on different crystallographic sites of the Mo-Ni-Re σ phase was found to be governed by the atomic sizes. Ni, having the smallest atomic size, showed a preference for low-coordination-number (CN) sites, whereas Mo, being the largest in atomic size, preferred occupying high-CN sites. However, the preference of Re, having intermediate atomic size, varied depending on the composition, and a clear reversal in the preference of Re as a function of the composition was evidenced in both the calculated and experimental site-occupancy results. [ABSTRACT FROM AUTHOR]

Complexes containing pyridine-2-carboxaldehyde (pyca) ligand acting as ?2-(N,O) chelates in [MX(CO)3(pyca)] (M = Mn, Re; X = Cl, Br), or [MoX(methallyl)(CO)2(pyca)] (X = Cl, Br), are good precursors for iminopyridine complexes derived from amino esters and peptides of formula [MX(CO)3(py-2-C(H)-NCHX-COOY)] or [MoX(methallyl)(CO)2(py-2-C(H)-NCHX-COOY)], via Schiff condensation of the aldehyde function of pyca with the terminal NH2 group of the amino ester or peptide. X-ray determinations confirm the structures and show that in solid phase the peptide chains assemble through H-bonds adopting different patterns which depend on the geometry of the metal-ligand fragments. The H-bonding patterns have been analyzed in detail and described by using graph set methods. In most cases, Mo complexes show intramolecular arrangement involving the halogen (Cl or Br) and an NH group of the side chain. For the Mn and Re complexes, the peptide side arms form infinite chains, helices, and rings. In many cases, the terminal carboxylic O-H function is engaged in a "terminal" H-bond with a polar molecule of solvent (THF or acetone), instead of forming the usual head-to-head arrangement found in simple carboxylic acids. For the longer tripeptide Gly-Gly-Gly, a discrete, dimeric association is observed, in which the peptide chains show antiparallel arrangement with a complementary disposition of the internal N-H and C-O functions. DOSY experiments in solution show significant changes in the diffusion rates upon addition of OPBu3, which indicate H-bonding interaction of OPBu3 with the peptide hydrogens. [ABSTRACT FROM AUTHOR]

Substitution of a methyl by a trifluoromethyl moiety in well-known β-ketimines afforded the ligands (Ar)NC(Me)CH2CO(CF3) (HLH, Ar = C6H5; HLMe, A r= 2,6-Me2C6H3; HLiPr, Ar = 2,6-iPr2C6H3). Subsequent complexation to the [MoO2]2+ core leads to the formation of novel complexes of general formula [MoO2(LR)2] (R = H, 1; R = Me, 2; R = iPr, 3). For reasons of comparison the oxo-imido complex [MoO(NtBu)(LMe)2] (4) has also been synthesized. Complexes 1-4 were investigated in oxygen atom transfer (OAT) reactions using the substrate trimethylphosphine. The respective products after OAT, the reduced MoIV complexes [MoO(PMe3)(LR)2] (R = H, 5; R = Me, 6; R = iPr, 7) and [Mo(NtBu)(PMe3)(LMe)2] (8), were isolated. All complexes have been characterized by NMR spectroscopy, and 1-4 also by cyclic voltammetry. A positive shift of the MoVI-MoV reduction wave upon fluorination was observed. Furthermore, molecular structures of complexes 2, 4, 5, and 8 have been determined via single crystal X-ray diffraction analysis. Complex 8 represents a rare example of a MoIV phosphino-imido complex. Kinetic measurements by UV-vis spectroscopy of the OAT reactions from complexes 1-4 to PMe3 showed them to be more efficient than previously reported nonfluorinated ones, with ligand L' = (Ar)NC(Me)CH2CO(CH3) [MoO2(L')2] (9) and [MoO(NtBu)(L')2] (10), respectively. Thermodynamic activation parameters ΔH‡ and ΔS‡ of the OAT reactions for complexes 2 and 4 have been determined. The activation enthalpy for the reaction employing 2 is significantly smaller (12.3 kJ/mol) compared to the reaction with the nonfluorinated complex 9 (60.8 kJ/mol). The change of the entropic term ΔS‡ is small. The reaction of the oxo-imido complex 4 to 8 revealed a significant electron-donating contribution of the imido substituent. [ABSTRACT FROM AUTHOR]

Catecholates and 2-amidophenoxides are prototypical "noninnocent" ligands which can form metal complexes where the ligands are best described as being in the monoanionic (imino)semiquinone or neutral (imino)quinone oxidation state instead of their closed-shell dianionic form. Through a comprehensive analysis of structural data available for compounds with these ligands in unambiguous oxidation states (109 amidophenolates, 259 catecholates), the well-known structural changes in the ligands with oxidation state can be quantified. Using these correlations, an empirical "metrical oxidation state" (MOS) which gives a continuous measure of the apparent oxidation state of the ligand can be determined based on least-squares fitting of its C-C, C-O, and C-N bond lengths to this single parameter (a simple procedure for doing so is provided via a spreadsheet in the Supporting Information). High-valent d0 metal complexes, particularly those of vanadium(V) and molybdenum(VI), have ligands with unexpectedly positive, and generally nonintegral, MOS values. The structural effects in these complexes are attributed not to electron transfer, but rather to amidophenoxide- or catecholate-to-metal π bonding, an interpretation supported by the systematic variation of the MOS values as a function of the degree of competition with the other π-donating groups in the structures. [ABSTRACT FROM AUTHOR]

The 2,2'-biphenyl-bridged bis(2-aminophenol) ligand 4,4'-di-tert-butyl-N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-2,2'-diaminobiphenyl (tBuClipH4) reacts with MoO2(acac)2 to form (tBuClipH2)MoO2, where the diarylamines remain protonated and bind trans to the terminal oxo groups. This complex readily loses water on treatment with pyridine or 3,5-lutidine to form mono-oxo complexes (tBuClip)MoO(L), which exhibit predominantly a cis-β geometry with an aryloxide trans to the oxo group. Exchange of the pyridine ligands is rapid and takes place by a dissociative mechanism, which occurs with retention of stereochemistry at molybdenum. Oxo-free alkoxide complexes (tBuClip)Mo(OR)2 are formed from (tBuClipH2)MoO2 and ROH. Treatment of NMo(OtBu)3 with tBuClipH4 results in complete deprotonation of the bis(aminophenol) and formation of a dimolybdenum complex (tBuClip)Mo(μ-N)(μ-NH2)Mo(tBuClip) containing both a bridging nitride (Mo-N = 1.848 Å, Mo-N-Mo = 109.49°) and a bridging amide group. The strong π bonding of this bis(amidophenoxide) ligand allows the molybdenum center to interconvert readily among species forming three, two, one, or zero π bonds from multiply bonded ligands. [ABSTRACT FROM AUTHOR]

The preparation and oxygen-atom-transfer (OAT) reactivity of oxoimido complexes [MoO(N-t-Bu)(t-Bu2-4-Rpz)2] [where R = H (1), Br (2), and Me (3); t-Bu2pz = 3,5-di-tert-butylpyrazolate] are reported. The reaction of the potassium salt of the respective pyrazolate ligands and the molybdenum oxoimido precursor, [MoO(N-t-Bu)Cl2(dme)] (dme = dimethoxyethane), in toluene afforded complexes 1–3 in good yields. The complexes were fully characterized by 1H and 13C NMR and IR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray crystallography. The solid-state structures reveal that, in each case, the molybdenum center is coordinated by one oxo, one N-t-Bu group, and two sterically demanding pyrazolate ligands via their two adjacent nitrogen atoms in an η2 fashion. Coordination around the metal center is severely distorted from octahedral and might be seen as closely approaching a distorted trigonal-prismatic geometry, which is relevant to the active site of dimethyl sulfoxide reductase in its oxidized form. The potential utility of all of the complexes 1–3 for OAT reactivity toward PMe3 at room temperature is examined, and plausible mechanistic pathways are explored by density functional theory calculations. Furthermore, the complexes reported here open a new and convenient entry into mixed oxoimidomolybdenum complexes. [ABSTRACT FROM AUTHOR]

An extensive series of heterometal-iron-sulfur single cubane-type clusters with core oxidation levels [MFe3S3Q]3+,2+ (M = Mo, W; Q = S, Se) has been prepared by means of a new method of cluster self-assembly. The procedure utilizes the assembly system [(tBu3tach)MVIS3]/FeCl2/Na2Q/NaSR in acetonitrile/THF and affords product clusters in 30-50% yield. The trisulfido precursor acts as a template, binding FeII under reducing conditions and supplying the MS3 unit of the product. The system leads to specific incorporation of a μ3-chalcogenide from an external source (Na2Q) and affords the products [(tBu3tach)MFe3S3QL3]0/1- (L = Cl-, RS-), among which are the first MFe3S3Se clusters prepared. Some 16 clusters have been prepared, 13 of which have been characterized by X-ray structure determinations including the incomplete cubane [(tBu3tach)MoFe2S3Cl2(μ2-SPh)], a possible trapped intermediate in the assembly process. Comparisons of structural and electronic features of clusters differing only in atom Q at one cubane vertex are provided. In comparative pairs of complexes differing only in Q, placement of one selenide atom in the core increases core volumes by about 2% over the Q = S case, sets the order Q = Se > S in Fe-Q bond lengths and Q = S > Se in Fe-Q-Fe bond angles, causes small positive shifts in redox potentials, and has an essentially nil effect on 57Fe isomer shifts. Iron mean oxidation states and charge distributions are assigned to most clusters from isomer shifts. (tBu3tach = 1,3,5-tert-butyl-1,3,5-triazacyclohexane) [ABSTRACT FROM AUTHOR]

Synthetic studies are presented addressing the oxidative decarbonylation of molybdenum and tungsten complexes supported by the encumbering m-terphenyl isocyanide ligand CNArDipP2 (ArDipP2 = 2,6-(2,6-(i-Pr)2C6H3)2C6H3). These studies represent an effort to access halide or pseudohalide M/CNArDipp2 species (M = Mo, W) for use as precursors to low-coordinate, low-valent group 6 isocyanide complexes. The synthesis and structural chemistry of the tetra- and tricarbonyl tungsten complexes trans-W(CO)4(CNArDipp2)2 and trans-W(NCMe)(CO) 3 (CNArDipp2)2 are reported. The acetonitrile adducts trans-M(NCMe)(CO) 3 (CNArDipp2)2 (M = Mo, W) react with I2 to form divalent, diiodide complexes in which the extent of decarbonylation differs between Mo and W. In the molybdenum example, the diiodide, dicarbonyl complex MoI2 (CO)2(CNArDipp2)2 is generated, which has an S = 1 ground state in solution. Paramagnetic group 6 MX2L4 complexes are rare, and the structure of MoI2 (CO)2(CNArDipp2)2 is discussed in relation to other diamagnetic and C2v-distorted MX2L4 complexes. Diiodide MoI2 (CO)2(CNArDipp2)2 reacts further with I2 to effect complete decarbonylation, producing the paramagnetic tetraiodide complex trans-MoI4 (CNArDipp2)2. The reactivity of the trans-M(NCMe)(CO) 3 (CNArDipp2)2 (M = Mo, W) complexes toward benzoyl peroxide is also surveyed, and it is shown that dicarboxylate complexes can be obtained by oxidative or salt-elimination routes. The reduction behavior of the tetraiodide complex trans-MoI4(CNArDipp2)2 toward Mg metal and sodium amalgam is studied. In benzene solution under N2, trans-MoI4(CNArDipp2)2 is reduced by Na/Hg to the η6-arene-dinitrogen complex, (η6-C6H6)Mo(N2)(CNArDipp2)2. The diiodide-η 6-benzene complex (η 6-C6H6)MoI2 (CNArDipp2)2 is an isolable intermediate in this reduction reaction, and its formation and structure are discussed in context of putative low-coordinate, low-valent molybdenum isocyanide complexes. [ABSTRACT FROM AUTHOR]

The reaction of 3 equiv of the ligand 2-[(2-chlorophenyl)azo]pyridine (La) or 2-[(4-chlorophenyl)azo]pyridine (Lb) with 1 equiv of Cr(CO)6 or Mo(CO)6 in boiling n-octane afforded [Cr(La/b)3]0 (1a and 1b) and [Mo(La/b)3]0 (2a and 2b). The chemical oxidation reaction of these neutral complexes with I2 in CH2Cl2 provided access to air-stable one-electron-oxidized species as their triiodide (I3-) salts. The electronic structures of chromium and molybdenum centers coordinated by the three redox noninnocent ligands La/b along with their redox partners have been elucidated by using a host of physical methods: X-ray crystallography, magnetic susceptibility measurements, nuclear magnetic resonance, cyclic voltammetry, absorption spectroscopy, electron paramagnetic resonance spectroscopy, and density functional theory. The four representative complexes, 1a, [1a]I3, 2a, and [2a]I3, have been characterized by X-ray crystallography. The results indicate a predominant azo-anion-radical description of the ligands in the neutral chromium(III) species, [CrIII(L′-)3], affording a singlet ground state through strong metal-ligand antiferromagnetic coupling. All of the electrochemical processes are ligand-based; i.e., the half-filled (t2g)3 set of the CrIII d3 ion remains unchanged throughout. The description of the molybdenum analogue is less clear-cut because mixing between metal- and ligand-based orbitals is more significant. On the basis of variations in net spin densities and orbital compositions, we argue that the oxidation events are again primarily ligand-based, although the electron density at the molybdenum center is clearly more variable than that at the chromium center in the corresponding series [1a]+, 1a, and [1a]-. [ABSTRACT FROM AUTHOR]

A model system for the molybdenum cofactor has been developed that illustrates the noninnocent behavior of an N-heterocycle appended to a dithiolene chelate on molybdenum. The pyranopterin of the molybdenum cofactor is modeled by a quinoxalyldithiolene ligand (S2BMOQO) formed from the reaction of molybdenum tetrasulfide and quinoxalylalkyne. The resulting complexes TEA[Tp*MoX(S2BMOQO)] [1, X = S; 3, X = O; TEA = tetraethylammonium; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate] undergo a dehydration-driven intramolecular cyclization within quinoxalyldithiolene, forming Tp*MoX(pyrrolo-S2BMOQO) (2, X = S; 4, X = O). 4 can be oxidized by one electron to produce the molybdenum(5+) complex 5. In a preliminary report of this work, evidence from X-ray crystallography, electronic absorption and resonance Raman spectroscopies, and density functional theory (DFT) bonding calculations revealed that 4 possesses an unusual asymmetric dithiolene chelate with significant thione-thiolate character. The results described here provide a detailed description of the reaction conditions that lead to the formation of 4. Data from cyclic voltammetry, additional DFT calculations, and several spectroscopic methods (IR, electronic absorption, resonance Raman, and electron paramagnetic resonance) have been used to characterize the properties of members in this suite of five Mo(S2BMOQO) complexes and further substantiate the highly electron-withdrawing character of the pyrrolo-S2BMOQO ligand in 2, 4, and 5. This study of the unique noninnocent ligand S2BMOQO provides examples of the roles that the N-heterocycle pterin can play as an essential part of the molybdenum cofactor. The versatile nature of a dithiolene appended by heterocycles may aid in modulating the redox processes of the molybdenum center during the course of enzyme catalysis. [ABSTRACT FROM AUTHOR]

Valuable information on the active sites of molybdenum enzymes has been provided from both MoV electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS). One of three major categories of MoV EPR signals from the molybdenum enzyme sulfite oxidase is the low-pH signal, which forms in the presence of chloride. Two alternative structures for this species have been proposed, one in which the chloride is coordinated directly to Mo and a second in which chloride is held in the arginine-rich basic pocket some 5 Å from Mo. Here we present an independent assessment of the structure of this species by using XAS of the analogous bromide and iodide complexes. We show that there is no evidence of direct Mo-I coordination, and that the data are consistent with a structure in which the halide is bound at ~5 Å from Mo. [ABSTRACT FROM AUTHOR]

The encapsulation of the complex [Ni(dto)2]2- within an oxothiododecamolybdic cyclic cluster has been investigated. The resulting molybdenum ring, [Mo12O12S12(OH)12(Ni(dto)2)]2-, corresponds to the first example of the {Mo2O2S2}-based assembly arranged around a 3d transition-metal complex. It was unambiguously characterized in the solid state and in solution by FT-IR spectroscopy, single-crystal X-ray diffraction, NMR, UV—visible spectroscopy, and electrospray ionization-high-resolution mass spectrometry (ESI-HRMS). The latter technique revealed to be a powerful tool for the characterization of templated molybdenum ring systems in solution and gave excellent results in high resolution. The electronic spectrum of [Mo12O12S12(OH)12(Ni(dto)2)]2- evidenced a strong red shift of the LMCT bands attributed to the complex [Ni(dto)2]2-, suggesting significant variations of the electronic properties upon its encapsulation within the Mo12 ring. These differences were demonstrated by electrochemical studies in CH3CN, which also revealed, for both compounds [Ni(dto)2]2- and [Mo12O12S12(OH)12(Ni(dto)2)]2-, electrocatalytic properties for the reduction of protons. These results evidence the ability of dithioxalato complexes to act as electrocatalysts for the hydrogen evolution reaction (HER) and confirm such a property for oxothiomolybdenum rings. [ABSTRACT FROM AUTHOR]

A new series of compounds identified in the phase diagram of ZrO2—V2O5—MoO3 have been synthesized via the solution combustion method. Single crystals of one of the compounds in the series, ZrV1.50Mo0.50O7.25, were grown by the melt-cool technique from the starting materials with double the MoO3 quantity. The room temperature average crystal structure of the grown crystals was solved using the single crystal X-ray diffraction technique. The crystals belong to the cubic crystal system, space group Pα3– (No. 205) with α = 8.8969 (4) Å, V = 704.24 (6) Å3, and Z = 4. The final R1 value of 0.0213 was achieved for 288 independent reflections during the structure refinement. The Zr4+ occupies the special position (4α) whereas V5+ and Mo6+ occupy two unique (8c) Wyckoff positions. Two fully occupied O atoms, (24d) and (4b), one partially occupied O atom (8c) have been identified for this molybdovanadate, which is a unique feature for these crystals. The structure is related to both ZrV2O7 and cubic ZrMo2O8. The temperature dependent single crystal studies show negative thermal expansion above 370 K. The compounds have been characterized by powder X-ray diffraction, solid-state UV—vis diffuse reflectance spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activity of these compounds has been investigated for the degradation of various dyes, and these compounds show specificity toward the degradation of non-azoic dyes. [ABSTRACT FROM AUTHOR]

The molecular and electronic structures and bonding analysis of terminal cationic metal-ylyne complexes (MeCN)(PMe3)4M≡EMes]+ (M = Mo, W; E = Si, Ge, Sn, Pb) were investigated using DFT/BP86/TZ2P/ZORA level of theory. The calculated geometrical parameters for the model complexes are in good agreement with the reported experimental values. The M-E σ-bonding orbitals are slightly polarized toward E except in the complex [(MeCN)(PMe3)4W(SnMes)]+, where the M-E σ-bonding orbital is slightly polarized toward the W atom. The M-E π-bonding orbitals are highly polarized toward the metal atom. In all complexes, the π-bonding contribution to the total M≡EMes bond is greater than that of the σ-bonding contribution and increases upon going from M = Mo to W. The values of orbital interaction ΔEorb are significantly larger in all studied complexes I-VIII than the electrostatic interaction ΔEelstat. The absolute values of the interaction energy, as well as the bond dissociation energy, decrease in the order Si > Ge > Sn > Pb, and the tungsten complexes have stronger bonding than the molybdenum complexes. [ABSTRACT FROM AUTHOR]