Structures of Mo2Oy- and Mo2Oy (y=2, 3, and 4) studied by anion photoelectron spectroscopy and density functional theory calculations

The competitive structural isomers of the Mo(2)O(y) (-)Mo(2)O(y) (y=2, 3, and 4) clusters are investigated using a combination of anion photoelectron (PE) spectroscopy and density functional theory calculations. The PE spectrum and calculations for MoO(3) (-)MoO(3) are also presented to show the level of agreement to be expected between the spectra and calculations. For MoO(3) (-) and MoO(3), the calculations predict symmetric C(3v) structures, an adiabatic electron affinity of 3.34 eV, which is above the observed value 3.17(2) eV. However, there is good agreement between observed and calculated vibrational frequencies and band profiles. The PE spectra of Mo(2)O(2) (-) and Mo(2)O(3) (-) are broad and congested, with partially resolved vibrational structure on the lowest energy bands observed in the spectra. The electron affinities (EA(a)s) of the corresponding clusters are 2.24(2) and 2.33(7) eV, respectively. Based on the calculations, the most stable structure of Mo(2)O(2) (-) is Y shaped, with the two Mo atoms directly bonded. Assignment of the Mo(2)O(3) (-) spectrum is less definitive, but a O-Mo-O-Mo-O structure is more consistent with overall electronic structure observed in the spectrum. The PE spectrum of Mo(2)O(4) (-) shows cleanly resolved vibrational structure and electronic bands, and the EA of the corresponding Mo(2)O(4) is determined to be 2.13(4) eV. The structure most consistent with the observed spectrum has two oxygen bridge bonds between the Mo atoms.     

MoO3/SiO2催化剂的异丁烷选择氧化反应性能

分别采用浸渍法和溶胶－凝胶法制备了MoO3/SiO2催化剂，用XRD，TPR，IR，TPD和活性评价等手段对催化剂的影响，晶格氧活泼性，化学吸附性能和异丁烷选择氧化反应性能进行了研究。结果表明，催化剂表面由Lewis碱位Mo=M,Mo-O-Mo中的晶格氧和Lewis酸位Mo^6 构成，在MoO3/SiO2催化剂上，异丁烷主要通过甲基的H双位吸附在表面的Lewis碱位Mo=O上；在常压条件下，异丁烷选择氧化产物主要为异丁烷，甲基丙烯醛和甲基丙烯酸，其中深度氧化产物CO2主要由吸附的异丁烯继续反应生成；采用溶胶－凝胶法制备的MoO3/SiO2催化剂，可得到较高的异丁烷转化率和含氧有机物选择性。     

Reactivity studies of oxo-Mo(IV) complexes containing potential hydrogen-bond acceptor/donor phenolate ligands

Reactivity studies of oxo-Mo(IV) complexes, Tp(iPr)MoO{2-OC(6)H(4)C(O)R-κ(2)O,O'} (R = Me, Et, OMe, OEt, OPh, NHPh), containing chelated hydrogen-bond donor/acceptor phenolate ligands are reported. Hydrolysis/oxidation of Tp(iPr)MoO(2-OC(6)H(4)CO(2)Ph-κ(2)O,O') in the presence of methanol yields tetranuclear [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2) (1), while condensation of Tp(iPr)MoO{2-OC(6)H(4)C(O)Me-κ(2)O,O'} and methylamine gives the chelated iminophenolate complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κ(2)O,N} (2), rather than the aqua complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κO}(OH(2)). The oxo-Mo(IV) complexes are readily oxidized by dioxygen or hydrogen peroxide to the corresponding cis-dioxo-Mo(VI) complexes, Tp(iPr)MoO(2){2-OC(6)H(4)C(O)R}; in addition, suitable one-electron oxidants, e.g., [FeCp(2)]BF(4) and [N(C(6)H(4)Br)(3)][SbCl(6)], oxidize the complexes to their EPR-active (g(iso) ≈ 1.942) molybdenyl counterparts (3, 4). Molybdenyl complexes such as Tp(iPr)MoOCl{2-OC(6)H(4)C(O)R} (5) and Tp(iPr)MoOCl(2) also form when the complexes react with chlorinated solvents. The ester derivatives (R = OMe, OEt, OPh) react with propylene sulfide to form cis-oxosulfido-Mo(VI) complexes, Tp(iPr)MoOS{2-OC(6)H(4)C(O)R}, that crystallize as dimeric μ-disulfido-Mo(V) species, [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (6-8). The crystal structures of [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2), Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe}, Tp(iPr)MoOCl{2-OC(6)H(4)C(O)NHPh}·{2-HOC(6)H(4)C(O)NHPh}, and [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (R = OMe, OEt) are reported.     

Hydrothermal Synthesis, Crystal Structure and Fluorescent Property of a Novel Mo(Ⅴ) Phosphate [Zn(Mov6P4O31H10)2(C4H14N3)2]·2C4H13N3·8H2O

A new molybdenum phosphate [Zn(Mov6P4O31H10)2(C4H14N3)2]·2C4H13N3·8H2O 1 (C4H13N3 = diethylenetriamine) has been synthesized under hydrothermal condition. Single-crystal X-ray diffraction reveals that compound 1 crystallizes in the monoclinic, space group P21/n, a =13.1679(3), b = 22.1240(6), c = 13.6146(3) (A), β = 103.4847(7)°, V = 3856.95(16) (A)3,C16H90N12O70P8ZnMo12, Mr = 3035.41, Z = 2, Dc = 2.614 g/cm3, μ = 2.483 mm-1, F(000) = 2968, S = 1.014, the final R = 0.0196 and wR = 0.0506 for 7486 observed reflections (I ＞ 2σ(Ⅰ)). Compound 1 consists of two identical rings of six edge-sharing MoO6 octahedra interconnected by one ZnO6 octahedron, whereas the PO4 tetrahedra which share their apices with the MoO6 octahedra are only located on one side of each Mo6 ring. The 2-charge of polyanion [Zn(Mov6P4O31H10)2]2- unit is compensated in the crystal by two mono-protonated diethylenetriamines (C4H14N3)+. By hydrogen bonding interactions the polyanion of compound 1 is interconnected to form pseudo three dimensional molybdophosphate. Other characterizations by elemental analyses, IR spectrum and fluorescent spectrum are also described.     

Hydrothermal Synthesis,Crystal Structure and Fluorescent Property of a Novel Mo(V) Phosphate [Zn(Mo~v_6P_4O_(31)H_(10))_2(C_4H_(14)N_3)_2]·2C_4H_(13)N_3·8H_2O

1 INTRODUCTION Hydrothermal synthesis of Mo(V) phosphates has allowed various structures, all characterized by the presence of identical clusters with the composition Mo12MP8X62 (X = O, OH) to be stabilized[1～6]. Many Mo(V) phosphates with such clusters have been iso- lated to date. The first compound was discovered by Haushalter and Lai[1] for M = Na with the formula (PPh4)2[(H3O)2NaMo6P4O24(OH)7]?5H2O. Recently, a second type of structure has been observed for M = Na (Na8(…     

Controllable synthesis of organic-inorganic hybrid MoOx/polyaniline nanowires and nanotubes

A novel chemical oxidative polymerization approach has been proposed for the controllable preparation of organic-inorganic hybrid MoO(x)/polyaniline (PANI) nanocomposites based on the nanowire precursor of Mo(3)O(10)(C(6)H(8)N)(2)·2H(2)O with sub-nanometer periodic structures. The nanotubes, nanowires, and rambutan-like nanoparticles of MoO(x)/PANI were successfully obtained through simply modulating the pH values to 2.5-3.5, ≈2.0 and ≈1.0, respectively. Through systematic physicochemical characterization, such as scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and so forth, the composition and structure of MoO(x)/PANI hybrid nanocomposites are well confirmed. It is found that the nanowire morphology of the precursor is the key to achieve the one-dimensional (1D) structures of final products. A new polymerization-dissolution mechanism is proposed to explain the formation of such products with different morphologies, in which the match between polymerization and dissolution processes of the precursor plays the important role. This approach will find a new way to controllably prepare various organic-inorganic hybrid 1D nanomaterials especially for polymer-hybrid nanostructures.     

Molybdenum(VI) catalysts obtained from η3-allyl dicarbonyl precursors: synthesis, characterization and catalytic performance in cyclooctene epoxidation

The oxidative decarbonylation of the η(3)-allyl dicarbonyl complexes [Mo(η(3)-C(3)H(5))Cl(CO)(2)(L)] (L = 2,2'-bipyridine (bipy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tert-butylhydroperoxide (TBHP) or H(2)O(2) gave the following compounds in good to excellent yields: the oxo-bridged dimers [MoO(2)Cl(L)](2)O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH(3)CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO(3)(bipy)][MoO(3)(H(2)O)]}(n) (4) and the octanuclear complex [Mo(8)O(24)(di-tBu-bipy)(4)] (7) using TBHP(50 equiv.)/H(2)O/70 °C; the oxodiperoxo complexes MoO(O(2))(2)(L) (L = bipy (5), di-tBu-bipy (8)) using H(2)O(2)(10 equiv.)/CH(3)CN/r.t. The structure of 7·x(solvent) (where solvent = CH(2)Cl(2) and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7·10CH(2)Cl(2), the crystal structure of 7·x(solvent) is unique due to differences in the crystal packing. Compounds 1-8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H(2)O(2) as oxidant at 55 or 70 °C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 °C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3-5)/TBHP, complex 5 from (1,3-5)/H(2)O(2), and complex 8 from (2,6-8)/H(2)O(2). With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 °C) were obtained using excess H(2)O as solvent (28-38% for 1,3-5; 87-98% for 2,6-8), while with H(2)O(2) as oxidant, the highest epoxide yields were obtained using CH(3)CN as solvent (54-81% for 3-8).     

阶跃过渡应答技术研究Mo-V/Al_2O_3催化剂上乙烷氧化脱氢制乙烯反应的暂态动力学 Ⅰ.C_2H_6,O_2,C_2H_4和CO_2在催化剂上的吸附行为

用阶跃过渡应答技术研究了乙烷氧化脱氢反应的反应物C_2H_6,O_2,产物C_2H_4和主要副产物CO_2在MoO_3-V_2O_5/Al_2O_3催化剂上的吸附行为。结果表明:C_2H_6和C_2H_4在该催化剂上不吸附;氧为慢吸附、不可逆吸附;CO_2为可逆吸附,吸附量较小。并发现在无氧的条件下,乙烷能与催化剂表面上的晶格氧反应生成乙烯。这些结果对乙烷氧化脱氢反应机理的探讨有重要意义。     

Sulfido-bridged dinuclear molybdenum-copper complexes related to the active site of CO dehydrogenase: [(dithiolate)Mo(O)S2Cu(SAr)]2- (dithiolate = 1,2-S2C6H4, 1,2-S2C6H2-3,6-Cl2, 1,2-S2C2H4)

The [MoCu] carbon monoxide dehydrogenase (CODH) is a Cu-containing molybdo-flavoprotein, the active site of which contains a pterin-dithiolene cofactor bound to a sulfido-bridged dinuclear Mo-Cu complex. In this paper, the synthesis and characterization of dinuclear Mo-Cu complexes relevant to the active site of [MoCu]-CODH are described. Reaction of [MoO2S2]2- with CuCN affords the dinuclear complex [O2MoS2Cu(CN)]2- (1), in which the CN- ligand can be replaced with various aryl thiolates to give rise to a series of dinuclear complexes [O2MoS2Cu(SAr)]2- (Ar = Ph (2), o-Tol (3), and p-Tol (4)). An alternative synthesis of complex 2 is the reaction of [MoO2S2]2- with [Cu(SPh)3]2-. Similarly, [O2MoS2Cu(PPh3)]- (5), [O2MoS2Cu(dppe)]- (dppe = 1,2-bis(diphenylphosphino)ethane) (6), and [O2MoS2Cu(triphos)]- (triphos = 1,1,1-tris[(diphenylphosphino)methyl]ethane) (7) were prepared from the reactions of [MoO2S2]2- with the Cu(I) phosphine complexes. Treatment of 1, 2, 4, or 5 with dithiols (1,2-(SH)2C6H4, 1,2-(SH)2C6H2-3,6-Cl2, and 1,2-(SH)2C2H4), in acetonitrile, leads to the replacement of a molybdenum-bound oxo ligand to yield [(dithiolate)Mo(O)S2CuL]2- (L = CN, SAr; dithiolate = 1,2-S2C6H4, 1,2-S2C6H2-3,6-Cl2, or 1,2-S2C2H4) (8-13) or [(1,2-S2C6H4)Mo(O)S2Cu(PPh3)]- (14) complexes.     

Further evidence for the tetraoxoiodate(V) anion,IO(4)(3-): hydrothermal syntheses and structures of Ba[(MoO(2))(6)(IO(4))(2)O(4)] x H(2)O and Ba(3)[(MoO(2))(2)(IO(6))(2)] x 2H(2)O

The hydrothermal reaction of MoO(3) with BaH(3)IO(6) at 180 degrees C for 3 days results in the formation of Ba[(MoO(2))(6)(IO(4))(2)O(4)] x H(2)O (1). Under similar conditions, the reaction of Ba(OH)(2) x 8H(2)O with MoO(3) and Ba(IO(4))(2) x 6H(2)O yields Ba(3)[(MoO(2))(2)(IO(6))(2)] x 2H(2)O (2). The structure of 1, determined by single-crystal X-ray diffraction, consists of corner- and edge-sharing distorted MoO(6) octahedra that create two-dimensional slabs. Contained within this molybdenum oxide framework are approximately C(2v) tetraoxoiodate(V) anions, IO(4)(3-), that are involved in bonding with five Mo(VI) centers. The two equatorial oxygen atoms of the IO(4)(3-) anion chelate a single Mo(VI) center, whereas the axial atoms are mu(3)-oxo groups and complete the octahedra of four MoO(6) units. The coordination of the tetraoxoiodate(V) anion to these five highly electropositive centers is probably responsible for stabilizing the substantial anionic charge of this anion. The Ba(2+) cations separate the layers from one another and form long ionic contacts with neighboring oxygen atoms and a water molecule. Compound 2 also contains distorted MoO(6) octahedra. However, these solely edge-share with octahedral hexaoxoiodate(VII), IO(6)(5-), anions to form zigzagging one-dimensional, (1)(infinity)[(MoO(2))(IO(6))](3-), chains that are polar. These chains are separated from one another by Ba(2+) cations that are coordinated by additional water molecules. Bond valence sums for the iodine atoms in 1 and 2 are 5.01 and 7.03, respectively. Crystallographic data: 1, monoclinic, space group C2/c, a = 13.584(1) A, b = 7.3977(7) A, c = 20.736(2) A, beta = 108.244(2) degrees, Z = 4; 2, orthorhombic, space group Fdd2, a = 13.356(7) A, b = 45.54(2) A, c = 4.867(3) A, Z = 8.     

Hybrid organic-inorganic 1D and 2D frameworks with epsilon-Keggin polyoxomolybdates as building blocks

Organic-inorganic hybrid materials based on polyoxometalate building blocks with capping La3+ ions and bidentate oxygenated ligands have been obtained by reaction at room temperature of the [epsilon-PMo12O36(OH)4[La(H2O)4]]5+ polyoxocation with glutarate (C5H6O(2)(2-)) and squarate (C4O(4)(2-)) organic ligands. [epsilon-PMo12O37(OH)3[La(H2O)4(C5H6O4)0.5]4].21 H2O (1) and [epsilon-PMo12O39(OH)[La(H2O)6]2-[La(H2O)5(C4O4)0.5]2].17 H2O (2) form unprecedented 1D chains built from alternating polyoxocations and organic ligands connected through LaO links. The structures of these materials are compared to the 2D hybrid organic-inorganic framework [NC4H12]2-[Mo22O52(OH)18[La(H2O)4]2[La(CH3CO2)2]4].8H2O (3) isolated from the hydrothermal reaction of elemental precursors (MoO(4)(2-), Mo, La3+) in acetate buffer. Compound 3 is built from previously undescribed polyoxometalate units with twenty-two MoV centers capped by six La3+ ions, four of which are bridged by acetate ligands.     

cis-Dioxomolybdenum(VI) and oxo(phosphine oxide)molybdenum(IV) complexes: steric and electronic fine-tuning of cis-[MoOS]2+ precursors

The complexes cis-Tp(iPr)Mo(VI)O2(OAr) (Tp(iPr) = hydrotris(3-isopropylpyrazol-1-yl)borate, -OAr = phenolate or naphtholate derivative) are formed upon metathesis of Tp(iPr)MoO2Cl and HOAr/NEt3 in dichloromethane. The orange, diamagnetic dioxo-Mo(VI) complexes exhibit strong nu(MoO2) IR bands at ca. 930 and 905 cm(-1) and NMR spectra indicative of C(s) symmetry. They undergo electrochemically reversible, one-electron reductions at potentials in the range -0.714 to -0.855 V vs SCE (in MeCN) and react with PEt3 to produce Tp(iPr)Mo(IV)O(OAr)(OPEt3). The green, diamagnetic oxo-Mo(IV) complexes display a single nu(MoO) IR band at ca. 950 cm(-1) and exhibit NMR spectra indicative of C1 symmetry. The crystal structures of eight dioxo-Mo(VI) complexes have been determined to assess the degree of frontal (O3-donor face) steric congestion at the Mo center, to identify complexes amenable to conversion into monomeric oxosulfido-Mo(VI) derivatives. The complexes display distorted octahedral geometries, with a cis arrangement of terminal oxo ligands, with d(Mo=O)av = 1.694 A and angle(MoO2)av = 103.4 degrees. Maximal frontal steric congestion is observed in the 2-phenolate derivatives, and these are identified as precursors for strictly monomeric(solid and solution state) oxosulfido-Mo(VI) counterparts.     

Synthesis of Lower Valent Molybdenum Oxides by an Ambient Temperature Reduction of Aqueous K(2)MoO(4) by KBH(4)

Reduction of aqueous K(2)MoO(4) with aqueous KBH(4) at ambient temperatures has been investigated systematically to obtain lower valent molybdenum oxides. Several lower valent oxides such as MoO(2), Mo(4)O(11), K(0.26)MoO(3) (red bronze), K(0.30)MoO(3) (blue bronze), and K(0.85)Mo(6)O(17) are formed during the reduction process; however, only MoO(2) has been obtained as single-phase product. The nature of the product formed is strongly influenced by the reducing power of KBH(4). The reducing power increases with decreasing pH or increasing concentration and volume of KBH(4). The as-prepared samples are amorphous as revealed by X-ray diffraction and transmission electron microscopy. They crystallize sharply at around 350-500 degrees C as revealed by differential scanning calorimetry. Since the products formed are amorphous in nature, they may become particularly attractive for battery electrodes and catalysis.     

Reaction mechanism of naphthyl radicals with molecular oxygen. 1. Theoretical study of the potential energy surface

Potential energy surfaces (PESs) of the reactions of 1- and 2-naphthyl radicals with molecular oxygen have been investigated at the G3(MP2,CC)//B3LYP/6-311G** level of theory. Both reactions are shown to be initiated by barrierless addition of O(2) to the respective radical sites of C(10)H(7). The end-on O(2) addition leading to 1- and 2-naphthylperoxy radicals exothermic by 45-46 kcal/mol is found to be more preferable thermodynamically than the side-on addition. At the subsequent reaction step, the chemically activated 1- and 2-C(10)H(7)OO adducts can eliminate an oxygen atom leading to the formation of 1- and 2-naphthoxy radical products, respectively, which in turn can undergo unimolecular decomposition producing indenyl radical + CO via the barriers of 57.8 and 48.3 kcal/mol and with total reaction endothermicities of 14.5 and 10.2 kcal/mol, respectively. Alternatively, the initial reaction adducts can feature an oxygen atom insertion into the attacked C(6) ring leading to bicyclic intermediates a10 and a10' (from 1-naphthyl + O(2)) or b10 and b10' (from 2-naphthyl + O(2)) composed from two fused six-member C(6) and seven-member C(6)O rings. Next, a10 and a10' are predicted to decompose to C(9)H(7) (indenyl) + CO(2), 1,2-C(10)H(6)O(2) (1,2-naphthoquinone) + H, and 1-C(9)H(7)O (1-benzopyranyl) + CO, whereas b10 and b10' would dissociate to C(9)H(7) (indenyl) + CO(2), 2-C(9)H(7)O (2-benzopyranyl) + CO, and 1,2-C(10)H(6)O(2) (1,2-naphthoquinone) + H. On the basis of this, the 1-naphthyl + O(2) reaction is concluded to form the following products (with the overall reaction energies given in parentheses): 1-naphthoxy + O (-15.5 kcal/mol), indenyl + CO(2) (-123.9 kcal/mol), 1-benzopyranyl + CO (-97.2 kcal/mol), and 1,2-naphthoquinone + H (-63.5 kcal/mol). The 2-naphthyl + O(2) reaction is predicted to produce 2-naphthoxy + O (-10.9 kcal/mol), indenyl + CO(2) (-123.7 kcal/mol), 2-benzopyranyl + CO (-90.7 kcal/mol), and 1,2-naphthoquinone + H (-63.2 kcal/mol). Simplified kinetic calculations using transition-state theory computed rate constants at the high-pressure limit indicate that the C(10)H(7)O + O product channels are favored at high temperatures, while the irreversible oxygen atom insertion first leading to the a10 and a10' or b10 and b10' intermediates and then to their various decomposition products is preferable at lower temperatures. Among the decomposition products, indenyl + CO(2) are always most favorable at lower temperatures, but the others, 1,2-C(10)H(6)O(2) (1,2-naphthoquinone) + H (from a10 and b10'), 1-C(9)H(7)O (1-benzopyranyl) + CO (from a10'), and 2-C(10)H(7)O (2-benzopyranyl) + O (from b10 and minor from b10'), may notably contribute or even become major products at higher temperatures.     

Production of C6O6- from oligomerization of CO on molybdenum anions

C6O6- has been observed in mass spectra of the anionic reaction products between small molybdenum suboxide clusters and carbon monoxide. No other free oxocarbanions were observed, nor were any dianions. The anion photoelectron spectrum of C6O6- shows that the neutral has an adiabatic electron affinity of 2.54(5) eV and an excited triplet state with a term energy of 1.0(1) eV. Analysis of the mass spectra suggests that C6O6- may be forming from oligomerization of CO on bare or highly reduced molybdenum anion centers.     

Monodithiolene molybdenum(V, VI) complexes: a structural analogue of the oxidized active site of the sulfite oxidase enzyme family

The active sites of the xanthine oxidase and sulfite oxidase enzyme families contain one pterin-dithiolene cofactor ligand bound to a molybdenum atom. Consequently, monodithiolene molybdenum complexes have been sought by exploratory synthesis for structural and reactivity studies. Reaction of [MoO(S(2)C(2)Me(2))(2)](1-) or [MoO(bdt)(2)](1-) with PhSeCl results in removal of one dithiolate ligand and formation of [MoOCl(2)(S(2)C(2)Me(2))](1-) (1) or [MoOCl(2)(bdt)](1-) (2), which undergoes ligand substitution reactions to form other monodithiolene complexes [MoO(2-AdS)(2)(S(2)C(2)Me(2))](1-) (3), [MoO(SR)(2)(bdt)](1-) (R = 2-Ad (4), 2,4,6-Pr(i)(3)C(6)H(2) (5)), and [MoOCl(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (6) (Ad = 2-adamantyl, bdt = benzene-1,2-dithiolate). These complexes have square pyramidal structures with apical oxo ligands, exhibit rhombic EPR spectra, and 3-5 are electrochemically reducible to Mo(IV)O species. Complexes 1-6 constitute the first examples of five-coordinate monodithiolene Mo(V)O complexes; 6 approaches the proposed structure of the high-pH form of sulfite oxidase. Treatment of [MoO(2)(OSiPh(3))(2)] with Li(2)(bdt) in THF affords [MoO(2)(OSiPh(3))(bdt)](1-) (8). Reaction of 8 with 2,4,6-Pr(i)(3)C(6)H(2)SH in acetonitrile gives [MoO(2)(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (9, 55%). Complexes 8 and 9 are square pyramidal with apical and basal oxo ligands. With one dithiolene and one thiolate ligand of a square pyramidal Mo(VI)O(2)S(3) coordination unit, 9 closely resembles the oxidized sites in sulfite oxidase and assimilatory nitrate reductase as deduced from crystallography (sulfite oxidase) and Mo EXAFS. The complex is the first structural analogue of the active sites in fully oxidized members of the sulfite oxidase family. This work provides a starting point for the development of both structural and reactivity analogues of members of this family.     

New chloro,mu-oxo,and alkyl derivatives of dioxomolybdenum(VI) and -tungsten(VI) complexes chelated with N(2)O tridentate ligands: synthesis and catalytic activities toward olefin epoxidation

A new series of cis-dioxomolybdenum(VI) complexes MoO(2)(L(n))Cl (n = 1-5) were prepared by the reaction of MoO(2)Cl(2)(DME) (DME = 1,2-dimethoxyethane) with 2-N-(2-pyridylmethyl)aminophenol (HL(1)) or its N-alkyl derivatives (HL(n)) (n = 2-5) in the presence of triethylamine. The new mu-oxo dimolybdenum compounds [MoO(2)(L(n))](2)O (n = 1, 4, 5, 7) were also prepared by treating the corresponding ligand HL(n) with MoO(2)(acac)(2) (acac = acetylacetonate) in warm methanolic solutions or (NH(4))(6)[Mo(7)O(24)].4H(2)O in the presence of dilute HCl. Treatment of MoO(2)(L(1))Cl or [MoO(2)(L(1))](2)O with the Grignard reagent Me(3)SiCH(2)MgCl gave the alkyl compound MoO(2)(L(1))(CH(2)SiMe(3)), which represents the first example of dioxomolybdenum(VI) alkyl complex supported by a N(2)O-type ancillary ligand. The analogous chloro and mu-oxo tungsten derivatives WO(2)(L(n))Cl (n = 6, 7) and [WO(2)(L(n))](2)O (n = 1, 4, 6, 7) were prepared by the reaction of WO(2)Cl(2)(DME) with HL(n) in the presence of triethylamine. Similar to their molybdenum analogues, the tungsten alkyl complexes WO(2)(L(n))(R) (n = 6, 7; R = Me, Et, CH(2)SiMe(3), C(6)H(4)(t)Bu-4) were synthesized by treating WO(2)(L(n))Cl or [WO(2)(L(n))](2)O (n = 6, 7) with the appropriate Grignard reagents. The catalytic properties of selected dioxo-Mo(VI) and -W(VI) chloro and mu-oxo complexes toward epoxidation of styrene by tert-butyl hydroperoxide (TBHP) were also investigated.     

Visible absorption spectrum of the CH3CO radical

The visible absorption spectrum of the acetyl radical, CH(3)CO, was measured between 490 and 660 nm at 298 K using cavity ring-down spectroscopy. Gas-phase CH(3)CO radicals were produced using several methods including: (1) 248 nm pulsed laser photolysis of acetone (CH(3)C(O)CH(3)), methyl ethyl ketone (MEK, CH(3)C(O)CH(2)CH(3)), and biacetyl (CH(3)C(O)C(O)CH(3)), (2) Cl + CH(3)C(O)H --> CH(3)C(O) + HCl with Cl atoms produced via pulsed laser photolysis or in a discharge flow tube, and (3) OH + CH(3)C(O)H --> CH(3)CO + H(2)O with two different pulsed laser photolysis sources of OH radicals. The CH(3)CO absorption spectrum was assigned on the basis of the consistency of the spectra obtained from the different CH(3)CO sources and agreement of the measured rate coefficients for the reaction of the absorbing species with O(2) and O(3) with literature values for the CH(3)CO + O(2) + M and CH(3)CO + O(3) reactions. The CH(3)CO absorption spectrum between 490 and 660 nm has a broad peak centered near 535 nm and shows no discernible structure. The absorption cross section of CH(3)CO at 532 nm was measured to be (1.1 +/- 0.2) x 10(-19) cm(2) molecule(-1) (base e).     

Molybdenum(VI) dioxo and oxo-imido complexes of fluorinated β-ketiminato ligands and their use in OAT reactions

Substitution of a methyl by a trifluoromethyl moiety in well-known β-ketimines afforded the ligands (Ar)NC(Me)CH(2)CO(CF(3)) (HL(H), Ar = C(6)H(5); HL(Me), A r= 2,6-Me(2)C(6)H(3); HL(iPr), Ar = 2,6-(i)Pr(2)C(6)H(3)). Subsequent complexation to the [MoO(2)](2+) core leads to the formation of novel complexes of general formula [MoO(2)(L(R))(2)] (R = H, 1; R = Me, 2; R = iPr, 3). For reasons of comparison the oxo-imido complex [MoO(N(t)Bu)(L(Me))(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 Mo(IV) complexes [MoO(PMe(3))(L(R))(2)] (R = H, 5; R = Me, 6; R = iPr, 7) and [Mo(N(t)Bu)(PMe(3))(L(Me))(2)] (8), were isolated. All complexes have been characterized by NMR spectroscopy, and 1-4 also by cyclic voltammetry. A positive shift of the Mo(VI)-Mo(V) 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 Mo(IV) phosphino-imido complex. Kinetic measurements by UV-vis spectroscopy of the OAT reactions from complexes 1-4 to PMe(3) showed them to be more efficient than previously reported nonfluorinated ones, with ligand L' = (Ar)NC(Me)CH(2)CO(CH(3)) [MoO(2)(L')(2)] (9) and [MoO(N(t)Bu)(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.     

Peroxomolybdate(VI)-citrate and -malate complex interconversions by pH-dependence. Synthetic, structural and spectroscopic studies

The reaction of potassium molybdate(VI) with biologically relevant ligands, citric and malic acids, in the presence of H2O2 was investigated for the effect of pH variations on the product pattern. That with citric acid led to the formation of the monomeric complex K4[MoO(O2)2(cit)].4H2O (1) in the pH range 7-9, and dimer K5[MoO(O2)(2-)(Hcit)H(Hcit)(O2)2OMo].6H2O (2) (H4cit = citric acid) at pH 3-6 through carboxylate-carboxylic acid hydrogen bonding. The relation with the previously identified K4[MoO3(cit)].2H2O (4) and K4[Mo2O5(Hcit)2].4H2O (5) were shown. These and other intermediates were shown to react in the pH range 3-6 to give a more stable species 2; the reaction sequence was demonstrated either by the protonation from 1 or the deprotonation of [MoO(O2)2(H2cit)](2-) (8). Evidence that 2 exists as a dimer in solution is presented. The reaction with (S)-malic acid afforded Delta-K(2n)[MoO(O2)2((S)-Hmal)]n.nH2O (3) (H3mal = malic acid) that was oxidized further to oxalato molybdate (11) by H2O2. The three complexes 1-3 were characterized by elemental analysis, UV, IR and NMR spectroscopies, in addition to the X-ray structural studies that show citrate and malate being coordinated as bidentate ligands via alpha-alkoxyl and alpha-carboxylate groups. The formation of these complexes is dictated by pH and their thermal stabilities varied with the coordinated hydroxycarboxylate ligands.