Terminal Oxo Ligands Research Articles

ChemInform Abstract: What Does It Really Take to Stabilize Complexes of Late Transition Metals with Terminal Oxo Ligands?

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What Does it Really Take to Stabilize Complexes of Late Transition Metals with Terminal Oxo Ligands?

Surprisingly stable: Noble-metal complexes with terminal oxo ligands are frequently postulated as intermediates, but they are generally considered elusive, as their d electrons destabilize the M=O units. Until recently, the isolation of such compounds was thought to require strong acceptor ligands, but now a remarkably stable Pt=O complex has been obtained employing a simple pincer ligand.

C−H Bond Cleavage with Reductants: Re-Investigating the Reactivity of Monomeric MnIII/IV−Oxo Complexes and the Role of Oxo Ligand Basicity

The thermodynamic properties of structurally similar Mn(III) and Mn(IV) complexes have been reinvestigated to understand their reactivity with substrates having C-H bonds. The complexes have the general formula [MnH(3)buea(O)](n-), where [H(3)buea](3-) is the tripodal ligand, tris[(N'-tert-butylureaylato)-N-ethylene]aminato. These complexes are unique because of the intramolecular hydrogen-bonding (H-bond) network surrounding the Mn-oxo units. The redox potentials for the Mn(III/IV)(O) couple was incorrectly assigned in earlier reports: the corrected value is -1.0 V vs Cp(2)Fe(+)/Cp(2)Fe in DMSO, while the Mn(IV/V)(O) process is -0.076 under the same conditions. The oxo ligand in the Mn(III)(O) complexes is basic with a pK(a) of 28.3; the basicity of the terminal oxo ligand in the Mn(IV)(O) complex is estimated to be approximately 15. These values were used to re-evalulate the O-H bond dissociation energy (BDE(OH)) of the corresponding Mn(II/III)-OH complexes: BDE(OH) values of 89 and 77 kcal/mol were determined for [Mn(III)H(3)buea(OH)](-) and [Mn(II)H(3)buea(OH)](2-), respectively. Both Mn(O) complexes react with 9,10-dihydroanthracene (DHA) to produce anthracene in nearly quantitative yields. This is surprising based on the low redox potiental of the complexes, suggesting the basicity of the oxo ligand is a major contributor to the observed reactivity. In contrast to the thermodynamic results, a comparative kinetic investigation found that the Mn(III)(O) complex reacts nearly 20 times faster than the Mn(IV)(O) complex. Activation parameters, determined from an Eyring analysis, found that the entropy of activation is significantly different between the two systems (DeltaDeltaS(++) = -35 eu, where DeltaDeltaS(++) = DeltaS(++)(Mn(IV)(O)) - DeltaS(++)(Mn(III)(O)). This unusual kinetic behavior can be explained in the context of the basicity of the oxo ligands that leads to different mechanisms: for [Mn(III)H(3)buea(O)](2-) a proton transfer-electron transfer mechanism is proposed, whereas for [Mn(IV)H(3)buea(O)](-) a hydrogen-atom transfer pathway is likely.

Observed enhancement of the reactivity of a biomimetic diiron complex by the addition of water - mechanistic insights from theoretical modeling

The biomimetic diiron complex [Fe(III)Fe(IV)(mu-O)(2)(5-Me(3)-TPA)(2)](ClO(4))(3) (TPA = tris(2-pyridylmethyl)amine) has been found to be capable of oxidizing 9,10-dihydroanthracene in a solution of acetonitrile. Addition of water up to 1 M makes the reaction 200 times faster, suggesting that the water molecule in some way activates the catalyst for more efficient substrate oxidation. It is proposed that the enhanced reactivity results from the coordination of a water molecule to the iron(III) half of the complex, converting the bis-mu-oxo structure of the diiron complex to a ring-opened form where one of the bridging oxo groups is transformed into a terminal oxo group on iron(IV). The suggested mechanism is supported by DFT (B3LYP) calculations and transition state theory. Two different computational models of the diiron complex are used to model the hydroxylation of cyclohexane to cyclohexanol. Model has a bis-mu-oxo diiron core (diamond core) while model represents the "open core" analogue with one bridging mu-oxo group, a terminal oxo ligand on iron(IV), and a water molecule coordinated to iron(III). The computational results clearly suggest that the terminal oxo group is more reactive than the bridging oxo group. The free energy of activation is 7.0 kcal mol(-1) lower for the rate limiting step when the oxidant has a terminal oxo group than when both oxo groups are bridging the irons.

Studies on bis(halogeno) dioxomolybdenum(VI)-bipyridine complexes: Synthesis and catalytic activity

Dioxomolybdenum(VI) complexes with the general formula [MoO2Cl2L2] (L2=3,3'-dimethyl-2,2'-bipyridine, 5,5'-dimethyl-2,2'-bipyridine, 6,6'-dimethyl-2,2'-bipyridine, 4,4'-dibromo-2,2'-bipyridine, 5,5'-dibromo-2,2'-bipyridine, 5,5'-diamino-2,2'-bipyridine; 5,5'-dinitro-2,2'-bipyridine; 5,5'-di-ethoxycarbonyl-2,2'-bipyridine; 6-phenyl-2,2'-bipyridine; 2,2':6',2''-terpyridine) have been prepared and characterised. [MoO2Cl2(5,5'-di-ethoxycarbonyl-2,2'-bipyridine)] has been examined by single crystal X-ray analysis. The complexes were applied as homogenous catalysts for the epoxidation of cyclooctene with tert-butyl hydroperoxide (TBHP) as oxidising agent. The new compounds show an overall high activity and are highly selective catalysts in the epoxidation of cyclooctene. The stability of the complexes and differences in the catalytic activity can be clearly attributed to electronic contributions of the functional groups on bipyridine ligands and to steric restrictions. DFT calculations have assisted in a better understanding of the stability of the complexes and are in agreement with experiment. The influence of the terminal oxo ligands and the Lewis base ligands on the Mo center keep the compounds on quite a stable level of electron density.

Evidence for a terminal Pt(iv)-oxo complex exhibiting diverse reactivity

Many important biological and chemical processes, including photocatalytic water oxidation to molecular oxygen (of interest as a route to artificial photosynthesis) and the activation of dioxygen on metal surfaces, are thought to involve transition metal terminal oxo complexes. Poverenov et al. now report the synthesis of a platinum based oxidizing reagent with potentially useful characteristics. It's a d6 Pt(IV) terminal oxo complex that is not stabilized by an electron accepting ligand framework, and so exhibits reactivity as both an inter- and intra-molecular oxygen donor and as an electrophile. It also undergoes water activation to produce a terminal dihydroxo complex, which may be of relevance to the mechanism of water oxidation and other catalytic reactions. Terminal oxo complexes of transition metals are important in biological and chemical processes, for example, the catalytic oxidation of organic molecules and the activation of dioxygen on metal surfaces are thought to involve oxo complexes. This paper explored the reactivity of a d6 Pt(IV) complex, a dn (n > 5) terminal oxo complex that is not stabilized by an electron withdrawing ligand framework. The complex exhibits reactivity as an inter- and intra-molecular oxygen donor and as an electrophile. Terminal oxo complexes of transition metals have critical roles in various biological and chemical processes1,2. For example, the catalytic oxidation of organic molecules3,4, some oxidative enzymatic transformations5,6,7, and the activation of dioxygen on metal surfaces8 are all thought to involve oxo complexes. Moreover, they are believed to be key intermediates in the photocatalytic oxidation of water to give molecular oxygen, a topic of intensive global research aimed at artificial photosynthesis and water splitting9,10,11,12,13. The terminal oxo ligand is a strong π-electron donor, so it readily forms stable complexes with high-valent early transition metals. As the d orbitals are filled up with valence electrons, the terminal oxo ligand becomes destabilized2. Here we present evidence for a dn (n > 5) terminal oxo complex that is not stabilized by an electron withdrawing ligand framework. This d6 Pt(iv) complex exhibits reactivity as an inter- and intramolecular oxygen donor and as an electrophile. In addition, it undergoes a water activation process leading to a terminal dihydroxo complex, which may be relevant to the mechanism of catalytic reactions such as water oxidation.

Hydrothermal Synthesis and Structural Characterization of the High‐Valent Ruthenium‐Containing Polyoxoanion [{PW11O39}2{(HO)RuIV–O–RuIV(OH)}]10–

AbstractThe high‐valent ruthenium‐containing [{PW11O39}2{(HO)RuIV–O–RuIV(OH)}]10– anion (1) has been synthesized by hydrothermal reaction and characterized by X‐ray diffraction, IR, multinuclear (31P and 183W) NMR spectroscopy andelectrochemistry. Single‐crystal analysis was carried outon Rb10[{PW11O39}2{(HO)RuIV–O–RuIV(OH)}]·21H2O, which crystallizes in the monoclinic system, space group P21/n, with a = 11.1912(14), b = 21.9257(12), c = 38.7310(96) Å, β = 94.682(19)°, V = 9472(3) Å3, Z = 4. Polyanion 1 consists of two lacunary [α‐PW11O39]7– anions connected by a linear {(HO)Ru–O–Ru(OH)}4+ unit. Each ruthenium ion achieves six‐coordination through interaction with two terminal oxo ligands from the lacuna of each [PW11O39]7– anion.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Dioxidobis(2-oxo-1,2-dihydropyridin-3-olato)molybdenum(VI)

In the title compound, [Mo(C5H4NO2)2O2], the MoVI atom exhibits a distorted octa­hedral coordination geometry formed by two terminal oxo ligands and two monoanionic O,O-bidentate pyridinone ligands. The two terminal oxo ligands lie in a cis arrangement, the ketonic O atoms of the pyridinone ligands are coordinated trans to the oxo ligands and the deprotonated hydroxyl O atoms are located trans to each other. The crystal structure contains inter­molecular N—H⋯O hydrogen bonds, C—H⋯O contacts and face-to-face π–π stacking inter­actions with an inter­planar separation of 3.25 (1) Å.

Spectroscopic and Electronic Structure Studies of Symmetrized Models for Reduced Members of the Dimethylsulfoxide Reductase Enzyme Family

Enzymes belonging to the dimethylsulfoxide reductase (DMSOR) family of pyranopterin Mo enzymes have a unique active-site geometry in the reduced form that lacks a terminal oxo ligand, unlike the reduced active sites of other pyranopterin Mo enzymes. Furthermore, the DMSOR family is characterized by the coordination of two pyranopterin-ene-1,2-dithiolate ligands in their active sites, which is distinctive among the other pyranopterin Mo enzymes but analogous to all of the currently known tungsten-containing enzymes. Electronic absorption, resonance Raman, and ground- and excited-state density functional calculations of symmetrized analogues of the reduced DMSOR active site ([NEt4][Mo(IV)(QAd)(S2C2Me2)2] where Ad = 2-adamantyl; Q = O, S, Se) have allowed for a detailed description of Mo-bisdithiolene electronic structure in the absence of a strong-field oxo ligand. The electronic absorption spectra are dominated by dithiolene S --> Mo charge-transfer transitions, and the totally symmetric Mo-S Raman stretch is observed at approximately 400 cm(-1) for all three complexes. These data indicate that the Mo-bisdithiolene bonding scheme in high-symmetry [Mo(QAd)(S2C2Me2)2]- complexes is not strongly perturbed by the apical QAd- ligands, but instead, the dithiolene ligands define the t(2g) ligand field splitting. The effects of conserved geometric distortions observed in DMSOR, relative to these high-symmetry models, were explored by spectroscopically calibrated bonding calculations, and the results are discussed within the context of electronic structure contributions to ground-state destabilization and transition-state stabilization. The specific electronic structure tuning of the endogenous amino acid ligation on the mechanism of DMSOR is also discussed.

A Mixed‐Valence, Hexadecamolybdenum Cluster With an MoVI Cubane “Jewel” in a “Setting” of Five MolybdateVI‐Linked Dinuclear MoV Units

The hexadecanuclear, mixed-valence cluster [Mo(16)O(42)(OH)(2)(3-iPrC(3)H(3)N(2))(12)].H(2)O (1), has been synthesized and characterized by X-ray crystallography, IR spectroscopy and mass spectrometry. The C(2)-symmetric complex consists of a cubane Mo(VI) (4)O(4) "jewel" held in a 10-point "setting" comprised of five dinuclear Mo(V) units tethered together by two tetrahedral Mo(VI) centers. The dinuclear units are ligated by twelve 3-isopropylpyrazole units that interact with the Mo--O framework through a network of hydrogen bonds. Structural parameters, charge requirements, and bond valence sum analyses support the assignment of +5 and +6 oxidation states to the dinuclear and cubane/tetrahedral Mo centers, respectively. Space filling models reveal that the pyrazole groups coat much of the surface of the molecule, apart from a number of oxo-rich seams that trace a chiral pattern across the surface. Complex 1 exhibits a unique structure that combines moieties generally atypical of polyoxometalates, viz., a Mo cubane containing only two terminal oxo ligands, and three distinct Mo(V) (2) units (including a 5-coordinate Mo center) tethered into a 10-point "setting" by tetrahedral Mo(VI) centers.

Toward Multifunctional Mo(VI−IV) Complexes: cis-Dioxomolybdenum(VI) Complexes Containing Hydrogen-Bond Acceptors or Donors

The complexes cis-TpiPrMoVIO2(OAr-R) (TpiPr=hydrotris(3-isopropylpyrazol-1-yl)borate, -OAr-R=hydrogen-bonding phenolate derivative) are formed upon reaction of TpiPrMoO2Cl, HOAr-R, and NEt3 in dichloromethane. The orange, diamagnetic, dioxo-Mo(VI) complexes exhibit strong nu(MoO2) IR bands at ca. 935 and 900 cm(-1) and NMR spectra indicative of Cs symmetry. They undergo electrochemically reversible, one-electron reductions at potentials in the range -0.836 to -0.598 V vs SCE; the only exception is the 2-CO2Ph derivative, which exhibits an irreversible reduction at -0.924 V. The complexes display distorted octahedral geometries, with a cis arrangement of terminal oxo ligands and with d(Mo=O)av=1.695 A and angle(MoO2)av=103.2 degrees. The R groups of the 2-CHO and 2-NHCOMe derivatives are directed away from the oxo groups and into a cleft in the TpiPr ligand; these derivatives are characterized by Mo-O-Cipso angles of ca. 131 degrees (conformation 1). The R group(s) in the 2-CO2Me and 2,3-(OMe)2 derivatives lie above the face of the three O-donor atoms (directed away from the TpiPr ligand) and the complexes display Mo-O-Cipso angles of 153.1(2) and 149.7(2) degrees, respectively (conformation 2). Conformations 1 and 2 are both observed in the positionally disordered 2-COMe and 2-COEt derivatives, the two conformers having Mo-O-Cipso angles of 130-140 and >150 degrees, respectively. The 3-COMe and 3-NEt2 derivatives have substituents that project away from the TpiPr ligand and Mo-O-Cipso angles of 134.2(2) and 147.7(2) degrees, respectively. Many of the complexes exhibit fluxional behavior on the NMR time scale, consistent with the rapid interconversion of two conformers in solution.

Computational Studies of EPR Parameters for Paramagnetic Molybdenum Complexes. II. Larger MoV Systems Relevant to Molybdenum Enzymes

The careful validation of modern density functional methods for the computation of electron paramagnetic resonance (EPR) parameters in molybdenum complexes has been extended to a number of low-symmetry MoV systems that model molybdoenzyme active sites. Both g and hyperfine tensors tend to be reproduced best by hybrid density functionals with about 30-40% exact-exchange admixture, with no particular spin contamination problems encountered. Spin-orbit corrections to hyperfine tensors are mandatory for quantitative and, in some cases, even for qualitative agreement. The g11 (g||) component of the g tensor tends to come out too positive when spin-orbit coupling is included only to leading order in perturbation theory. Compared to single-crystal experiments, the calculations reproduce both g- and hyperfine-tensor orientations well, both relative to each other and to the molecular framework. This is significant, as simulations of the EPR spectra of natural-abundance frozen-solution samples frequently do not allow a reliable determination of the hyperfine tensors. These may now be extracted based on the quantum-chemically calculated parameters. In a number of cases, revised simulations of the experimental spectra have brought theory and experiment into substantially improved agreement. Systems with two terminal oxo ligands, and to some extent with an oxo and a sulfido ligand, have been confirmed to exhibit particularly large negative Deltag33 shifts and thus large g anisotropies. This is discussed in the context of the experimental data for xanthine oxidase.

π-Donor/Acceptor Effect on Lindqvist Type Polyoxomolibdates Because of Various Multiple-Bonded Nitrogenous Ligands

The electronic structures of Lindqvist type functionalized polyoxometalates (POM) ([Mo6O18R]n- R=O, NO, NAr, NNAr, NNAr2; n=2, 3) have been investigated using density functional methods. We discuss the role of the replacement of terminal oxo ligands by pi-donor/acceptor multiple-bonded nitrogenous ligands on the basis of geometrical parameters, charge analyses, reactivity indexes, and vibrational spectra. The calculated reactivity indexes (chemical potential, electronegativity, hardness, and electrophilicity) indicate that the most reactive functionalized POMs are those substituted by pi-acceptor ligands. These pi-acceptor ligands induce a decrease in the hardness and an increase in the chemical potential and electrophilicity, thus increasing the reactivity. Our calculations are in reasonable agreement with reported experimental data.

High-Nuclearity Osmium Carbonyl Cluster Complexes Containing (6-Methylpyrid-2-yl)imido Ligands. Synthesis of Hepta-, Octa-, and Nonanuclear Derivatives

Three high-nuclearity osmium carbonyl cluster complexes, [Os7(μ5-κ2-ampy)(μ-CO)2(CO)17] (1), [Os8(μ3-Η)(μ-H)(μ5-κ2-ampy)(μ-CO)(CO)19] (2), and [Os9O(μ4-κ2-ampy)2(CO)18] (3) (H2ampy = 2-amino-6-methylpyridine), have been prepared by heating [Os3(CO)12] with 0.5 equiv of H2ampy in decane at reflux temperature. The trinuclear complex [Os3(μ-Η)(μ3-κ2-Hampy)(CO)9] is an intermediate in this reaction. The metallic skeletons of 1 and 2 can be described as mono- (1) or bi-face-capped (2), basal-edge-bridged, square pyramids, whereas that of compound 3 consists of a pentagonal bipyramid with two equatorial edges spanned by metal atoms. In the three clusters, the ampy ligands are attached to edge-bridging Ru atoms through their pyridine N atoms, while they also cap metallic squares (in 1 and 2) or triangles (in 3) through their imido N atom. An additional feature of compound 3 is that it contains a terminal oxo ligand, unprecedented in osmium carbonyl cluster chemistry.

Synthesis, Characterization, and Biomimetic Chemistry of cis-Oxosulfidomolybdenum(VI) Complexes Stabilized by an Intramolecular Mo(O)S···S Interaction

The reactions of jade-green Tp*MoIVO(S2PR2) [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; R = Et, Pri, Ph] with propylene sulfide produce ochre-red Tp*MoVIOS{SP(S)R2}. The complexes have been characterized by microanalysis, mass spectrometry, cyclic voltammetry, spectroscopy (IR, NMR, UV-vis, and X-ray absorption), and X-ray crystallography. The distorted-octahedral isopropyl and phenyl derivatives feature a tridentate fac-Tp* ligand, a terminal oxo ligand, and a unique five-membered Mo(=S){SP(=S)R2 ring moiety formed by a weak, intramolecular, bonding interaction between the Mo=S1 and (uncoordinated) S3=P moieties. The Mo=S1 [2.227(2) A (R = Pri) and 2.200(2) A (R = Ph)] and S1...S3 distances [2.396(3) A (R = Pri) and 2.383(2) A (R = Ph)] are indicative of a pi-bonded Mo=S1 unit and a weak (bond order ca. 1/3) S1...S3 interaction; the solid-state structures are maintained in solution according to S K-edge X-ray absorption data. The complexes react with excess cyanide to form thiocyanate and Tp*MoO(S2PR2), under anaerobic conditions, or Tp*MoO2(S2PR2), under aerobic conditions; the latter models the production of thiocyanate and desulfo molybdenum hydroxylases upon cyanolysis of molybdenum hydroxylases. The complexes react with triphenylphosphine to give Tp*MoO(S2PR2) and SPPh3, with cobaltocene or hydrosulfide ion to produce [Tp*MoVOS(S2PR2)]-, and with ferrocenium salts to yield [Tp*MoVO(S3PR2)]+; in the last two reactions, Mo(V) is produced by direct or induced internal redox reactions, respectively. The presence of the Mo(O)=S...S interaction does not radically lengthen the Mo=S bond in the complexes or preclude them from reactions typical of unperturbed oxosulfidomolybdenum(VI) complexes.

Preparation and Properties of a Monomeric MnIV−Oxo Complex

Manganese-oxo complexes have long been investigated because of their proposed roles in biological and chemical catalysis. However, there are few examples of monomeric complexes with terminal oxo ligands, especially those with oxomanganese(IV) units. A oxomanganese(IV) complex has been prepared from [MnIIIH3buea(O)]2- ([H3buea]3-, tris[(N'-tert-butylureaylato)-N-ethylene]aminato), a monomeric MnIII-O complex in which the oxo ligand arises from cleavage of dioxygen. Treating [MnIIIH3buea(O)]2- with [Cp2Fe]BF4 in either DMF at -45 degrees C or DMSO at room temperature produces [MnIVH3buea(O)]-: lambdamax = 635 nm; nu(Mn-16O) = 737 cm-1; nu(Mn-18O) = 709 cm-1; g = 5.15, 2.44, 1.63, D = 3.0 cm-1, E/D = 0.26, aMn = 66 G (A = 190 MHz). These spectroscopic properties support the assignment of a mononuclear MnIV-oxo complex with an S = 3/2 ground state. Density functional theory supports this assignment and the Jahn-Teller distortion around the high-spin MnIV center that would alter the molecular structure of [MnIVH3buea(O)]- from trigonal symmetry (as indicated by the highly rhombic EPR signal). [MnIVH3buea(O)]- is relatively unstable in DMSO, converting to [MnIIIH3buea(OH)]- via a proposed X-H bond cleavage. [MnIVH3buea(O)]- reacts with 1,2-diphenylhydrazine to from azobenzene (95% yield) and [MnIIIH3buea(OH)]-. The MnIV-oxo does not react with triphenyl- or tricyclohexylphosphine. However, O-atom transfer is observed with methyldiphenylphosphine and dimethylphenylphosphine, producing the corresponding phosphine oxides. These results illustrate the diverse reactivity of the MnIV-oxo unit.

Vanadium calixarene complexes as molecular models for supported vanadia

Reaction of dimethylated tert-butyl calix[4]arene, H 2 A Me2 , with O VCl 2(thf) 2 unexpectedly led to the isolation of Cl V IV A Me , 2, whose crystal structure was determined. Hence, one of the MeO–C bonds present in H 2 A Me2 has been cleaved and one equivalent of HCl eliminated leaving three phenolate and one phenolether function to coordinate at the V centre. 2 smoothly reacts with O 2 to give O V V A Me , B, i.e. the chloride ligand has been replaced by a terminal oxo ligand with concomitant oxidation of the vanadium atom to the oxidation state +5. B crystallises isostructurally with 2; crystallisation of a mixture of 2 and B even leads to crystals that contain both compounds beside each other. However, when B was co-crystallised together with H 2 A Me2 , from acetonitrile a different structure with a partial cone conformation was obtained. The mechanism by which B is formed from 2 is discussed. To obtain information concerning the fate of the chloride ligand in 2, a derivative, Ph 3SiO–V IV A Me , 3, has been synthesised and investigated with respect to its behaviour in the presence of O 2: it reacts the same way as 2.

Structure and Bonding in Monomeric Iron(III) Complexes with Terminal Oxo and Hydroxo Ligands

We report on the structure and bonding in the title iron(III) complexes, containing the tris[(N'-tert-butylureayl)-N-ethyl]amine ligand, with density functional theory techniques. In agreement with the experimental data, a high-spin electronic state is favored for all of the systems we considered. H bonds between the terminal oxo and hydroxo ligands and NH groups present in the organic ligand coordinated to the metal have a remarkable effect on the overall coordination geometry. In fact, the structure of model complexes without H bonds shows shorter Fe-O bond lengths. This is a consequence of the ability of the H bonds to stabilize a remarkable amount of electron density localized on the terminal oxo and hydroxo ligands. Energy analysis indicates that each H bond stabilizes the nonheme complexes by roughly 35 kJ/mol. Molecular orbital analysis indicates a reduction of two Fe-O bonding electrons on going from a complex with a terminal oxo ligand to a complex with a terminal hydroxo ligand. This reduction in the number of bonding electrons is also supported by frequency analysis.

Photoelectron Spectroscopy of Doubly and Singly Charged Group VIB Dimetalate Anions: M2O72‐, MM′O72‐, and M2O7‐ (M, M′: Cr, Mo, W).

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Photoelectron Spectroscopy of Doubly and Singly Charged Group VIB Dimetalate Anions: M2O72-, MM‘O72-, and M2O7- (M, M‘ = Cr, Mo, W)

We produced both doubly and singly charged Group VIB dimetalate species-M(2)O(7)(2-), MM'O(7)(2-), and M(2)O(7)(-) (M, M' = Cr, Mo, W)-using two different experimental techniques (electrospray ionization for the doubly charged anions and laser vaporization for the singly charged anions) and investigated their electronic and geometric structures using photoelectron spectroscopy and density functional calculations. Distinct changes in the electronic and geometric structures were observed as a function of the metal and charge state. The electron binding energies of the heteronuclear dianions MM'O(7)(2-) were observed to be roughly the average of those of their homonuclear counterparts (M(2)O(7)(2-) and M'(2)O(7)(2-)). Density functional calculations indicated that W(2)O(7)(2-), W(2)O(7)(-), and W(2)O(7) possess different ground-state structures: the dianion is highly symmetric (D(3d),(1)A(1g)) with a single bridging oxo ligand, the monoanion is a doublet (C(1), (2)A) with two bridging oxo ligands and a radical terminal oxo ligand, whereas the neutral is a singlet (C(1), (1)A) with two bridging oxo ligands and a terminal peroxo ligand. The combined experimental and theoretical study provides insights into the evolution of geometric and electronic structures as a function of charge state. The clusters identified might provide insights into the possible structures of reactive species present in early transition-metal oxide catalysts that are relevant to their reactivity and catalytic function.