Molybdenum(V) on an oxide string. Formation and solution stability of the linear complex (mu-trans-dioxo(tetraphenylporphyrinato)molybdenato(V))- bis(oxo(tetraphenylporphyrinato)molybdenum(V)) perchlorate

The unusual linear trinuclear complex [Mo3O4(TPP)3]+ is formed in solution upon the reaction of [MoO(TPP)-(OClO3)] with [[MoO(TPP)]2O], and an equilibrium between [Mo3O4(TPP)3]+ and its constituent species is rapidly established. Spectrophotometric experiments suggest that [Mo3O4(TPP)3]+ is the predominant species found in solutions resulting from the mixture of [MoO(TPP)(OClO3)] and [[MoO(TPP)]2O], and its formation is strongly favored (log K = 5.5 +/- 0.5 M-1). No evidence of higher oligomers has been observed. A mechanism for the formation of [Mo3O4(TPP)3]+ by the controlled hydrolysis of [MoO(TPP)(OClO3)] is proposed.     

New luminescent solids in the Ln-W(Mo)-Te-O-(Cl) systems

Solid-state reactions of lanthanide(III) oxide (and/or lanthanide(III) oxychloride), MoO3 (or WO3), and TeO2 at high temperature lead to eight new luminescent compounds with four different types of structures, namely, Ln2(MoO4)(Te4O10) (Ln = Pr, Nd), La2(WO4)(Te3O7)2, Nd2W2Te2O13, and Ln5(MO4)(Te5O13)(TeO3)2Cl3 (Ln = Pr, Nd; M = Mo, W). The structures of Ln2(MoO4)(Te4O10) (Ln = Pr, Nd) feature a 3D network in which the MoO4 tetrahedra serve as bridges between two lanthanide(III) tellurite layers. La2(WO4)(Te3O7)2 features a triple-layer structure built of a [La2WO4]4+ layer sandwiched between two Te3O72- anionic layers. The structure of Nd2W2Te2O13 is a 3D network in which the W2O108- dimers were inserted in the large tunnels of the neodymium(III) tellurites. The structures of Ln5(MO4)(Te5O13)(TeO3)2Cl3 (Ln = Pr, Nd; M = Mo, W) feature a 3D network structure built of lanthanide(III) ions interconnected by bridging TeO32-, Te5O136-, and Cl- anions with the MO4 (M = Mo, W) tetrahedra capping on both sides of the Ln4 (Ln = Pr, Nd) clusters and the isolated Cl- anions occupying the large apertures of the structure. Luminescent studies indicate that Pr2(MoO4)(Te4O10) and Pr5(MO4)(Te5O13)(TeO3)2Cl3 (M = Mo, W) are able to emit blue, green, and red light, whereas Nd2(MoO4)(Te4O10), Nd2W2Te2O13, and Nd5(MO4)(Te5O13)(TeO3)2Cl3 (M = Mo, W) exhibit strong emission bands in the near-IR region.     

A study on the stability of O2 on oxometalloporphyrins by the first principles calculations

The authors investigated the interaction of oxometalloporphyrins (MO(por))--specifically, MoO(por), WO(por), TiO(por), VO(por), and CrO(por)--with O(2) by using first principles calculations. MoO(por) and WO(por) undergo reactions with O(2); on the other hand, TiO(por), VO(por), and CrO(por) do not. Next, they compared the interaction of MoO(por) and WO(por) with O(2). Activation barriers for the reactions of MoO(por) and WO(por) with a side-on O(2) are small. For MoO(por)(O(2)), the activation barrier for the reverse reaction that liberates O(2) is also small; however, that for WO(por)(O(2)) is large. The experimental results that photoirradiation with visible light or heating of Mo (VI)O(tmp)(O(2)) regenerates Mo (VI)O(tmp) by liberating O(2) while W (VI)O(tmp)(O(2)) does not [J. Tachibana, T. Imamura, and Y. Sasaki, Bull. Chem. Soc. Jpn. 71, 363 (1998)] are explained by the difference in activation barriers of the reverse reactions. This means that bonds formed between the W atom and O(2) are stronger than those between the Mo atom and O(2). The bond strengths can be explained by differences in the energy levels between the highest occupied molecular orbital of MoO(por) and WO(por), which are mainly formed from the a orbitals of the central metal atom and pi(*) orbitals of O(2).     

Probing the electronic structure of [MoOS(4)](-) centers using anionic photoelectron spectroscopy

Using photodetachment photoelectron spectroscopy (PES) in the gas phase, we investigated the electronic structure and chemical bonding of six anionic [Mo(V)O](3+) complexes, [MoOX(4)](-) (where X = Cl (1), SPh (2), and SPh-p-Cl (3)), [MoO(edt)(2)](-) (4), [MoO(bdt)(2)](-) (5), and [MoO(bdtCl(2))(2)](-) (6) (where edt = ethane-1,2-dithiolate, bdt = benzene-1,2-dithiolate, and bdtCl(2) = 3,6-dichlorobenzene-1,2-dithiolate). The gas-phase PES data revealed a wealth of new electronic structure information about the [Mo(V)O](3+) complexes. The energy separations between the highest occupied molecular orbital (HOMO) and HOMO-1 were observed to be dependent on the O-Mo-S-C(alpha) dihedral angles and ligand types, being relatively large for the monodentate ligands, 1.32 eV for Cl and 0.78 eV for SPh and SPhCl, compared to those of the bidentate dithiolate complexes, 0.47 eV for edt and 0.44 eV for bdt and bdtCl(2). The threshold PES feature in all six species is shown to have the same origin and is due to detaching the single unpaired electron in the HOMO, mainly of Mo 4d character. This result is consistent with previous theoretical calculations and is verified by comparison with the PES spectra of two d(0) complexes, [VO(bdt)(2)](-) and [VO(bdtCl(2))(2)](-). The observed PES features are interpreted on the basis of theoretical calculations and previous spectroscopic studies in the condensed phase.     

Electronic spectral studies of molybdenyl complexes. 2. MCD spectroscopy of [MoOS4]- centers

Magnetic circular dichroism (MCD) and absorption spectroscopies have been used to probe the electronic structure of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] complexes (edt = ethane-1,2-dithiolate). The results of density functional calculations (DFT) on [MoO(SMe)4]- and [MoO(edt)2]- model complexes were used to provide a framework for the interpretation of the spectra. Our analysis shows that the lowest energy transitions in [MoVOS4] chromophores (S4 = sulfur donor ligand) result from S-->Mo charge transfer transitions from S valence orbitals that lie close to the ligand field manifold. The energies of these transitions are strongly dependent on the orientation of the S lone-pair orbitals with respect to the Mo atom that is determined by the geometry of the ligand backbone. Thus, the lowest energy transition in the MCD spectrum of [PPh4][MoO(p-SC6H4X)4] (X = H) occurs at 14,800 cm-1, while that in [PPh4][MoO(edt)2] occurs at 11,900 cm-1. The identification of three bands in the absorption spectrum of [PPh4][MoO(edt)2] arising from LMCT from S pseudo-sigma combinations to the singly occupied Mo 4d orbital in the xy plane suggests that there is considerable covalency in the ground-state electronic structures of [MoOS4] complexes. DFT calculations on [MoO(SMe)4]- reveal that the singly occupied HOMO is 53% Mo 4dxy and 35% S p for the equilibrium C4 geometry. For [MoO(edt)2]- the steric constraints imposed by the edt ligands result in the S pi orbitals being of similar energy to the Mo 4d manifold. Significant S pseudo-sigma and pi donation may also weaken the Mo identical to O bond in [MoOS4] centers, a requirement for facile active site regeneration in the catalytic cycle of the DMSO reductases. The strong dependence of the energies of the bands in the absorption and MCD spectra of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] on the ligand geometry suggests that the structural features of the active sites of the DMSO reductases may result in an electronic structure that is optimized for facile oxygen atom transfer.     

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.     

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.     

A novel open framework uranyl molybdate: synthesis and structure of (NH4)4[(UO2)5(MoO4)7](H2O)5

Single crystals of (NH(4))(4)[(UO(2))(5)(MoO(4))(7)](H(2)O)(5) have been synthesized hydrothermally using (NH(4))(6)Mo(7)O(24), (UO(2))(CH(3)COO)(2).2H(2)O, and H(2)O at 180 degrees C. The phase has been characterized by single-crystal X-ray diffraction using a merohedrally twinned single crystal: it is hexagonal, P6(1), a = 11.4067(5) A, c = 70.659(5) A, V = 7961.9(7) A(3), and Z = 6. The structure is based upon an open framework with composition [(UO(2))(5)(MoO(4))(7)](4-) that is composed of UO(7) pentagonal bipyramids that share vertexes with MoO(4) tetrahedra. The framework has large channels (effective pore size: 4.8 x 4.8 A(2)) parallel to the c axis and a system of smaller channels (effective pore size: 2.5 x 3.6 A(2)) parallel to [100], [110], [010], [110], [110], and [110]. The channels are occupied by NH(4)(+) cations and H(2)O molecules. The topological structure of the uranyl molybdate framework can be described either in terms of fundamental chains of UO(7) pentagonal bipyramids and MoO(4) tetrahedra or in terms of tubular building units parallel to the c axis.     

Electronic structures of WAlO(y) and WAlO(y) (-) (y = 2-4) determined by anion photoelectron spectroscopy and density functional theory calculations

The anion photoelectron spectra of WAlO(y) (-) (y = 2-4) are presented and assigned based on results of density functional theory calculations. The WAlO(2) (-) and WAlO(3) (-) spectra are both broad, with partially resolved vibrational structure. In contrast, the WAlO(4) (-) spectrum features well-resolved vibrational structure with contributions from three modes. There is reasonable agreement between experiment and theory for all oxides, and calculations are in particular validated by the near perfect agreement between the WAlO(4) (-) photoelectron spectrum and a Franck-Condon simulation based on computationally determined spectroscopic parameters. The structures determined from this study suggest strong preferential W-O bond formation, and ionic bonding between Al(+) and WO(y) (-2) for all anions. Neutral species are similarly ionic, with WAlO(2) and WAlO(3) having electronic structure that suggests Al(+) ionically bound to WO(y) (-) and WAlO(4) being described as Al(+2) ionically bound to WO(4) (-2). The doubly-occupied 3sp hybrid orbital localized on the Al center is energetically situated between the bonding O-local molecular orbitals and the anti- or non-bonding W-local molecular orbitals. The structures determined in this study are very similar to structures recently determined for the analogous MoAlO(y) (-)∕MoAlO(y) cluster series, with subtle differences found in the electronic structures [S. E. Waller, J. E. Mann, E. Hossain, M. Troyer, and C. C. Jarrold, J. Chem. Phys. 137, 024302 (2012)].     

Pi-acid/pi-base carbonyloxomolybdenum(IV) complexes and their oxomolybdenum(VI/IV) precursors

Brown TpiPrMoO(SR)(CO) (TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate; R = Et, iPr, Ph, p-tol, Bz) are formed when TpiPrMoO(SR)(NCMe) react with CO gas in toluene. The carbonyloxomolybdenum(IV) complexes exhibit nu(CO) and nu(Mo=O) IR bands at ca. 2025 and 935 cm(-1), respectively, and NMR spectra indicative of C(1) symmetry, with delta(C)(CO) ca. 250. The crystal structure of TpiPrMoO(SiPr)(CO), the first for a mononuclear carbonyloxomolybdenum complex, revealed a distorted octahedral geometry, with d(Mo=O) = 1.683(3) A, d(Mo-C) = 2.043(5) A, and angle(O=Mo-C) = 90.87(16) degrees . The blue-green acetonitrile precursors are generated by reacting cis-TpiPrMoO2(SR) with PPh3; they are unstable, display a single nu(Mo=O) IR band at ca. 950 cm(-1), and exhibit NMR spectra consistent with C1 symmetry. Red-brown cis-TpiPrMoO2(SR) (R = as above and tBu) are formed by metathesis of TpiPrMoO2Cl and HSR/NEt3 in dichloromethane. The complexes exhibit strong nu(MoO2) IR bands at ca. 925 and 895 cm(-1), and NMR spectra indicative of Cs symmetry; the isopropyl, p-tolyl, and benzyl derivatives possess distorted octahedral geometries, with d(Mo=O)(av) = 1.698 A and angle(MoO(2))(av) = 103.5 degrees.     

Photoelectron imaging of Ag(-)(H2O)x and AgOH(-)(H2O)y (x=1,2, y=0-4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.     

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.     

Tristhiolatomolybdenum nitrides, (RS)(3)Mo[triple bond]N where R = (i)Pr and (t)Bu,preparation, characterization and comparisons with related trialkoxymolybdenumnitrides

The addition of thiols to ((t)BuO)(3)Mo[triple bond]N in toluene leads to the formation of (RS)(3)Mo[triple bond]N compounds as yellow, air-sensitive compounds, where R = (i)Pr and (t)Bu. The single-crystal structure of ((t)BuS)(3)Mo[triple bond]N reveals a weakly associated dimeric structure where two ((t)BuS)(3)Mo[triple bond]N units (Mo-N = 1.61 A, Mo-S = 2.31 A (av)) are linked via thiolate sulfur bridges with long 3.03 A (av) Mo-S interactions. Density functional theory calculations employing Gaussian 98 B3LYP (LANL2DZ for Mo and 6-31G* for N, O, S, and H) have been carried out for model compounds (HE)(3)Mo[triple bond]N and (HE)(3)MoNO, where E = O and S. A comparison of the structure and bonding within the related series ((t)BuE)(3)Mo[triple bond]N and ((t)BuE)(3)MoNO is made for E = O and S. In the thiolate compounds, the highest energy orbitals are sulfur lone-pair combinations. In the alkoxides, the HOMO is the N 2p lone-pair which has M-N sigma and M-O pi* character for the nitride. As a result of greater O p pi to Mo pi interactions, the M-N pi orbitals of the Mo-N triple bond are destabilized with respect to their thiolate counterpart. For the nitrosyl compounds, the greater O p pi to Mo d pi interaction favors greater back-bonding to the nitrosyl pi* orbitals for the alkoxides relative to the thiolates. The results of the calculations are correlated with the observed structural features and spectroscopic properties of the related alkoxide and thiolate compounds.     

Novel acetate polyoxomolybdate "host" accommodating a zigzag-chainlike "guest" of five edge-shared sodium cations: Na(21)[[Na(5)(H(2)O)(14)]within[Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]].CH(3)COONa. approximately equal to 95H(2)O

A novel ESR-silent polyoxomolybdate Na(21)([Na(5)(H(2)O)(14)][Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]).CH(3)COONa.approximately equal to 90H(2)O (3) was simply synthesized in high yield by reducing an acidified aqueous solution of Na(2)MoO(4).2H(2)O and CH(3)COONa.3H(2)O. The structure of 3 is constructed by a 46-member crown-shaped anion, [Na(5)(H(2)O)(14)]within[Mo(V)(20)Mo(VI)(26)O(134)(OH)(10)(mu-CH(3)COO)(4)](21-), 3a, which is built up by three different but related building blocks in a new mode and further connected into layers via Na(+) and hydrogen bonds. Crystal data of compound 3: triclinic space group P(-1); a = 16.4065(3), b = 17.4236(2), c = 20.8247(3) A; alpha= 87.57, beta= 67.9810(10), gamma= 80.6970(10)o; V = 5445.08(14) A(3); Z = 1; D(calcd) = 2.902. Structure solution and refinement are based on 19014 reflections, R = 0.0750.     

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.     

A novel ligand modification and diamond-core molybdenum(IV) 2,6-bis(2,2-diphenyl-2-thioethyl)pyridinate(2-) complex

The reaction of Mo(VI)O(2)(L-NS(2)) [L-NS(2) = 2,6-bis(2,2-diphenyl-2-thioethyl)pyridinate(2-)] or Mo(V)(2)O(3)(L-NS(2))(2) with excess PPh(3) in N,N-dimethylformamide at 70 degrees C results in the formation of gray-green (L-NOS)Mo(IV)(mu-O)(mu-S)Mo(IV)(L-NS(2)) [L-NOS = 2-(2,2-diphenyl-2-thioethyl)-6-(2,2-diphenyl-2-oxoethyl)pyridinate(2-)] (1). The crystal structure of 1 revealed a dinuclear complex comprised of two trigonal bipyramidal Mo centers bridged along an axial-equatorial edge (the mu-O-mu-S vector) such that the Mo-N bonds are trans to the bridging atoms and are anti with respect to the Mo-Mo bond (d(Mo-Mo) = 2.5535(5) A); the remaining coordination sites are occupied by the S- and O-donor atoms of the L-NOS and L-NS(2) ligands. The diamond core is asymmetric, with Mo(1/2)-O(1) distances of 1.845(2) and 2.009(2) A and Mo(1/2)-S(1) distances of 2.374(1) and 2.230(1) A. Compound 1 is unique in possessing a planar, diamond-core unit devoid of terminal oxo ligation and a new tridentate L-NOS ligand formed via a novel intramolecular modification of the original L-NS(2) ligand.     

Formation of a spiral-shaped inorganic-organic hybrid chain, [Cu(II)(2,2'-bipy)(H(2)O)(2)Al(OH)(6)Mo(6)O(18)](n)()(n)()(-): influence of intra- and interchain supramolecular interactions

A novel chainlike coordination polymer [Cu(II)(2,2'-bipy)(H(2)O)(2)Al(OH)(6)Mo(6)O(18)](n)()(n)()(-), formed from a heteropolyanion [Al(OH)(6)Mo(6)O(18)](3)(-) as a building unit and a copper(II) complex fragment, [Cu(II)(2,2'-bipy)(H(2)O)(2)](2+), as a linker, provides the first example of an extended structure based on an Anderson type of polyanion and a transition metal complex with organic ligand. The intra- and interchain O-H.O hydrogen-bonding interactions are seemingly responsible for the spiral shape of this chain. Crystal data: triclinic space group Ponemacr;, a = 11.2253(18) A, b = 14.5194(17) A, c = 15.2672(10) A, alpha = 112.191(8) degrees, beta = 106.693(9) degrees, gamma = 93.916(13) degrees, and Z = 2.     

A Ferromagnetic Interaction between Cu(2+) Centers through a [CrO(4)](2-) Bridge: Crystal Structures and Magnetic Properties of [{Cu(acpa)}(2)(&mgr;-MO(4))] (M = Cr, Mo) (Hacpa = N-(1-Acetyl-2-propyridene)(2-pyridylmethyl)amine)

The reaction of [Cu(acpa)](+) with [MO(4)](2)(-) (Hacpa = N-(1-acetyl-2-propyridene)(2-pyridylmethyl)amine and M = Cr and Mo) in water-methanol or water-acetonitrile solution affords dinuclear copper(II) complexes with metalate bridges, [{Cu(acpa)}(2)(&mgr;-CrO(4))].4CH(3)OH.4H(2)O (1) and [{Cu(acpa)}(2)(&mgr;-MoO(4))].4H(2)O (2), respectively. The crystal structures and the magnetic properties have been studied. Complexes 1 and 2 are isomorphous and the structures are made up of discrete dimers in which two copper(II) ions are bridged by the [MO(4)](2)(-) anion. The coordination geometry about the copper(II) ions is square planar with a N(2)O chelate group from acpa and an oxygen atom from [MO(4)](2)(-). Magnetic susceptibility measurements for 1 revealed that a ferromagnetic interaction between copper(II) ions is propagated through the [CrO(4)](2)(-) bridge and the coupling constant (2J) was evaluated to be 14.6(1) cm(-)(1) (H = -2JS(1).S(2)). In 2, two copper(II) ions bridged by [MoO(4)](2)(-) anion are antiferromagnetically coupled with the 2J value of -5.1(4) cm(-)(1). The ferromagnetic interaction in 1 is explained by means of the orbital topology of frontier orbitals. Crystal data: 1, monoclinic, space group P2(1)/m, a = 8.349(2) ?, b = 17.616(3) ?, c = 10.473 ?, beta = 107.40(2) degrees, Z= 2; 2, monoclinic, space group P2(1)/m, a = 8.486(2) ?, b = 18.043(3) ?, c = 9.753(2) ?, beta = 95.82(2) degrees, Z = 2.     

Interplay between defect structure and catalytic activity in the Mo(10-x)V(x)O(y) mixed-oxide system

The Mo(10-x)V(x)O(y) solid-solution systems (0≤x≤10) were studied by electron paramagnetic resonance spectroscopy. The results show the existence of paramagnetic vanadyl VO(2+) species, whose concentration becomes maximal for Mo(5)V(5)O(y·). A quantitative analysis of the [VO(2+)] concentration as a function of the Mo/V ratio allows it to characterize the prevailing defect chemistry in the Mo(10-x)V(x)O(y) system. In this respect, the semi-conducting properties of Mo(10-x)V(x)O(y) are p-type in an interval of Mo(9)V(1)O(y)-Mo(5)V(5)O(y) and switch into n-type because of the conduction electrons in a composition range of Mo(5)V(5)O(y)-Mo(1)V(9)O(y). Highest catalytic activity is obtained when vanadium acts as an acceptor center and oxygen vacancies ν(··)(O) are formed for reasons of charge compensation. In addition to the surface, ν(··)(O) and VO(2+) centers in the bulk have to be considered too for heterogeneous catalysis.     

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.