Synthesis, structure, and catalytic oxidation chemistry from the first oxo-imido Schiff base metal complexes

The molybdenum oxo-imido complex, [Mo(O)(NtBu)Cl2(dme)] (1), was obtained from the reaction between [MoO2Cl2(dme)] and [Mo(NtBu)2Cl2(dme)]. Reactions between [Mo(O)(NR)Cl2(dme)] (where R = tBu or 2,6-iPr2C6H3) and the disodium Schiff base compounds Na(2)(3,5-tBu2)2salen, Na(2)(3,5-tBu2)2salpen, and Na(2)(7-Me)2salen afforded the first oxo-imido transition metal Schiff base complexes: [Mo(O)(NtBu)[(3,5-tBu2)2salen]] (2), [Mo(O)(NtBu)[(3,5-tBu2)2salpen]] (3), and [Mo(O)(N-2,6-iPr2C6H3)[(7-Me)2salen]] (4), respectively. The compounds [Mo(NtBu)2[(3,5-tBu2)2salpen]] (5) from [Mo(NtBu)2(NHtBu)2] and [Mo(N-2,6-iPr2C6H3)(2)[(7-Me)2salen]](6) from [Mo(N-2,6-iPr2C6H3)(2)(NHtBu)2] (7) are also reported. Compounds 1-7 were characterized by NMR, IR, and FAB mass spectroscopy while compounds 3, 4, and 5 were additionally characterized by X-ray crystallography. In conjunction with tBuOOH as oxidant, compound 3 is a catalyst for the oxidation of benzyl alcohol to benzaldehyde and cis-cyclooctene and 1-octene to the corresponding epoxides.     

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.     

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.     

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.     

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.     

Synthesis, structural elucidation, and application of a pyrazolylpyridine-molybdenum oxide composite as a heterogeneous catalyst for olefin epoxidation

The reaction of [MoO(2)Cl(2)(pypzEA)] (1) (pypzEA = ethyl[3-(pyridin-2-yl)-1H-pyrazol-1-yl]acetate) with water in a Teflon-lined stainless steel autoclave (100 °C) or in an open reflux system leads to the isolation of the molybdenum oxide/pyrazolylpyridine composite material [Mo(2)O(6)(HpypzA)] (2; HpypzA = [3-(pyridinium-2-yl)-1H-pyrazol-1-yl]acetate). The solid state structure of 2 was solved through single crystal and powder X-ray diffraction analyses in conjunction with information derived from FT-IR and (13)C CP MAS NMR spectroscopies and elemental analyses. In the asymmetric unit of 2, two crystallographically distinct Mo(6+) centers are bridged by a syn,syn-carboxylate group of HpypzA. The periodic repetition of these units along the a axis of the unit cell leads to the formation of a one-dimensional composite polymer, (∞)(1)[Mo(2)O(6)(HpypzA)]. The outstretched pyrazolylpyridine groups of adjacent polymers interdigitate to form a zipper-like motif, generating strong onset π-π contacts between adjacent rings of coordinated HpypzA molecules. The composite oxide 2 is a stable heterogeneous catalyst for liquid-phase olefin epoxidation.     

Hydrothermal synthesis, structure and quantum chemistry of transition metal complex supported by metal-oxo cluster [{Ni(phen)2}2(x-Mo8O26)]

A nickel-1,10-phenanthroline complex supported on an octamolybdate, [{Ni(phen)2}2(x- Mo8O26)], has been hydrothermally synthesized with MoO3, H2MoO4, Ni(OAc)2· 6H2O and 1,10-phenathroline (1,10-phen) as raw materials. The crystals of the compound belong to monoclinic P21/n space group, a = 1.2952(2), b = 1.6659(10), c = 1.3956(12) nm, b =106.273(8)°, V = 2.8906(5) nm3, Z = 2. 5604 observable reflections (I ＞2s(I)) were used for structure resolution and refinements to converge to final R1 = 0.0414, wR2 = 0.0815. The result of structure determination shows that the compound contains octamolybdate possessing a novel structure type (named as x-isomer). The feature of x-[Mo8O26]4- is that it is composed of Mo6O6 ring and two MoO6 octahedra located at cap positions on opposite faces. The Mo6O6 ring contains two octahedral and four trigonal-bipyramidal MoVI atoms. Each x-[Mo8O26]4- unit is bonded with two [Ni(phen)2]2+ through terminal oxygen atoms of octahedral and neighbouring trigonal-bipyramidal Mo atom in the Mo6O6 ring. IR and UV-Vis spectra of the compound were measured and its electronic structure was studied by EHMO method.     

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.     

Polymer-anchored peroxo compounds of vanadium(V) and molybdenum(VI): synthesis, stability, and their activities with alkaline phosphatase and catalase

We generated a series of new polymer-bound peroxo complexes of vanadium(V) and molybdenum(VI) of the type [VO(O(2))(2)(sulfonate)]-PSS [PSS = poly(sodium 4-styrene sulfonate)] (PV(3)), [V(2)O(2)(O(2))(4)(carboxylate)VO(O(2))(2)(sulfonate)]-PSSM [PSSM = poly(sodium styrene sulfonate-co-maleate)] (PV(4)), [Mo(2)O(2)(O(2))(4)(carboxylate)]-PA [PA = poly(sodium acrylate)] (PMo(1)), [MoO(O(2))(2)(carboxylate)]-PMA [PMA = poly(sodium methacrylate)] (PMo(2)), and [MoO(O(2))(2)(amide)]-PAm [PAm = poly(acrylamide)] (PMo(3)) by reacting V(2)O(5) (for PV(3) and PV(4)) or H(2)MoO(4) (for PMo(1), PMo(2), and PMo(3)) with H(2)O(2) and the respective water-soluble macromolecular ligand at pH 5-6. The compounds were characterized by elemental analysis (CHN and energy-dispersive X-ray spectroscopy), spectral studies (UV-vis, IR, (13)C NMR, (51)V NMR, and (95) Mo NMR), thermal (TGA) as well as scanning electron micrographs (SEM), and EDX analysis. It has been demonstrated that compounds retain their structural integrity in solutions of a wide range of pH values and are approximately 100 times weaker as substrate to the enzyme catalase relative to H(2)O(2), its natural substrate. The effect of the title compounds, along with previously reported compounds [V(2)O(2)(O(2))(4)(carboxylate)]-PA (PV(1)) and [VO(O(2))(2)(carboxylate)]-PMA (PV(2)) on rabbit intestine alkaline phosphatase (ALP) has been investigated and compared with the effect induced by the free diperoxometallates viz. Na[VO(O(2))(2)(H(2)O)] (DPV), [MoO(O(2))(2)(glycine)(H(2)O)] (DMo(1)), and [MoO(O(2))(2)(asparagine)(H(2)O)] (DMo(2)). It has been observed that although all the compounds tested are potent inhibitors of the enzyme, the polymer-bound and neat complexes act via distinct mechanisms. Each of the macromolecular compounds is a classical noncompetitive inhibitor of ALP. In contrast, the action of neat pV and heteroligand pMo compounds on the enzyme function is consistent with a mixed type of inhibition.     

Organic-inorganic hybrid materials: hydrothermal syntheses and structural characterization of bimetallic organophosphonate oxides of the type Mo/Cu/O/RPO(3)(2-)/organoimine

The hydrothermal reactions of a Cu(II) starting material, a molybdate source, 2,2'-bipyridine or terpyridine, and the appropriate alkyldiphosphonate ligand yield two series of bimetallic organophosphonate hybrid materials of the general types [Cu(n)(bpy)(m)Mo(x)O(y)(H(2)O)(p)[O(3)P(CH(2))(n)PO(3)](z)] and [Cu(n)(terpy)(m)Mo(x)O(y)(H(2)O)(p)[O(3)P(CH(2))(n)PO(3)](z)]. The bipyridyl series includes the one-dimensional materials [Cu(bpy)(MoO(2))(H(2)O)(O(3)PCH(2)PO(3))] (1) and [[Cu(bpy)(2)][Cu(bpy)(H(2)O)](Mo(5)O(15))(O(3)PCH(2)CH(2)CH(2)CH(2)PO(3))].H(2)O (5.H(2)O) and the two-dimensional hybrids [Cu(bpy)(Mo(2)O(5))(H(2)O)(O(3)PCH(2)PO(3))].H(2)O (2.H(2)O), [[Cu(bpy)](2)(Mo(4)O(12))(H(2)O)(2)(O(3)PCH(2)CH(2)PO(3))].2H(2)O (3.2H(2)O), and [Cu(bpy)(Mo(2)O(5))(O(3)PCH(2)CH(2)CH(2)PO(3))](4). The terpyridyl series is represented by the one-dimensional [[Cu(terpy)(H(2)O)](2)(Mo(5)O(15))(O(3)PCH(2)CH(2)PO(3))].3H(2)O (7.3H(2)O) and the two-dimensional composite materials [Cu(terpy)(Mo(2)O(5))(O(3)PCH(2)PO(3))] (6) and [[Cu(terpy)](2)(Mo(5)O(15))(O(3)PCH(2)CH(2)CH(2)PO(3))] (8). The structures exhibit a variety of molybdate building blocks including isolated [MoO(6)] octahedra in 1, binuclear subunits in 2, 4, and 6, tetranuclear embedded clusters in 3, and the prototypical [Mo(5)O(15)(O(3)PR)(2)](4-) cluster type in 5, 7, and 8. These latter materials exemplify the building block approach to the preparation of extended structures.     

Hydrothermal synthesis, crystal structure, conductivity, and thermal decomposition of [Cu(4,4'-bipy)(H2O)(Mo3O10)].H2O

The hydrothermal reaction of (NH(4))(6)Mo(7)O(24).4H(2)O, CuCl(2).2H(2)O, and 4,4'-bipyridine yields bipyridine-ligated copper-trimolybdate monohydrate [Cu(4,4'-bipy)(H(2)O)(Mo(3)O(10))].H(2)O in the monoclinic system with space group of C(2/c) and cell parameters of a = 15.335(2) A, b = 15.535(2) A, c = 15.106(2) A, beta = 101.162(2) degrees, V = 3530.7(9) A(3), and Z = 8. Its structure consists of one-dimensional infinite ([Mo3O10]2-)( infinity ) chains linked through [Cu2(H2O)2(4,4'-bipy)] units. The Mo-O chain contains distorted [MoO(6)] octahedra connected through corner-sharing oxygen atoms into infinite chains along the c direction and each chain is located in the channel formed by four adjacent crossing chains of [Cu(4,4'-bipy)(H2O)](n)(2n+). The crystal shows weak conductivity through Mo-O chain along the c direction and insulating property along either a or b direction. Furthermore, a crystalline bimetallic oxide, CuMo3O10, forms when the title compound undergoes thermal treatment in N(2) atmosphere after the complete removal of the ligands.     

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.     

Polyoxometalate-supported transition metal complexes and their charge complementarity: synthesis and characterization of [M(OH)6Mo6O18[Cu(Phen)(H2O)2]2][M(OH)6Mo6O18[Cu(Phen)(H2O)Cl]2].5H2O (M = Al(+, Cr3+)

Two Anderson-type heteropolyanion-supported copper phenanthroline complexes, [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2]1+ (1c) and [Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2]1- (1a) complement their charges in one of the title compounds [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2][Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5H2O [1c][1a].5 H2O 1. Similar charge complementarity exists in the chromium analogue, [Cr(OH)6Mo6O18[Cu(phen)(H2O)2]2][Cr(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5 H2O [2c][2a].5 H2O 2. The chloride coordination to copper centers of 1a and 2a makes the charge difference. In both compounds, the geometries around copper centers are distorted square pyramidal and those around aluminum/chromium centers are distorted octahedral. Three lattice waters, from the formation of intermolecular O-H.....O hydrogen bonds, have been shown to self-assemble into an "acyclic water trimer" in the crystals of both 1 and 2. The title compounds have been synthesized in a simple one pot aqueous wet-synthesis consisting of aluminum/chromium chloride, sodium molybdate, copper nitrate, phenanthroline, and hydrochloric acid, and characterized by elemental analyses, EDAX, IR, diffuse reflectance, EPR, TGA, and single-crystal X-ray diffraction. Both compounds crystallize in the triclinic space group P. Crystal data for 1: a = 10.7618(6), b = 15.0238(8), c = 15.6648(8) angstroms, alpha = 65.4570(10), beta = 83.4420(10), gamma = 71.3230(10), V = 2182.1(2) angstroms3. Crystal data for 2: a = 10.8867(5), b = 15.2504(7), c = 15.7022(7) angstroms, alpha = 64.9850(10), beta = 83.0430(10), gamma = 71.1570(10), V = 2235.47(18) angstroms3. In the electronic reflectance spectra, compounds 1 and 2 exhibit a broad d-d band at approximately 700 nm, which is a considerable shift with respect to the value of 650-660 nm for a square-pyramidal [Cu(phen)2L] complex, indicating the coordination of [M(OH)6Mo6O18]3- POM anions (as a ligand) to the monophenanthroline copper complexes to form POM-supported copper complexes 1c, 1a, 2c, and 2a. The ESR spectrum of compound 1 shows a typical axial signal for a Cu2+ (d9) system, and that of compound 2, containing both chromium(III) and copper(II) ions, may reveal a zero-field-splitting of the central Cr3+ ion of the Anderson anion, [Cr(OH)6Mo6O18]3-, with an intense peak for the Cu2+ ion.     

Synthesis, characterization, and photochromic properties of hybrid organic-inorganic materials based on molybdate, DABCO, and piperazine

Prompted by our interest in new photochromic organic-inorganic hybrid materials, the reactivity of [Mo7O24]6- toward a structure-directing reagent diamine such as 1,4-diazabicyclo[2.2.2]octane (DABCO) and piperazine (pipz) has been investigated, and three new molybdenum(VI)-containing compounds, namely, (H2DABCO)3[Mo7O24].4H2O (1), (H2DABCO)[Mo3O10].H2O (2), and (H2DABCO)2(NH4)2[Mo8O27].4H2O (3), have been synthesized and characterized. New synthetic routes to achieve the known compounds (H2DABCO)2(H2pipz)[Mo8O27] (4), (H2pipz)3[Mo8O27] (5), and (H2DABCO)2[Mo8O26].4H2O (6) are also reported. All of these compounds contain different poly(oxomolybdate) clusters, i.e., discrete [Mo7O24]6- blocks in 1, infinite polymeric chains 1/infinity[Mo3O10]2- in 2, 1/infinity[Mo8O27]6- in 3-5, and 1/infinity[Mo8O26]4- in 6, associated in a tridimensional assembly by hydrogen bonds with H2DABCO2+ and/or H2pipz2+ cations. Interconversion pathways and chemical factors affecting the stabilization of the different species are highlighted and discussed. At the opposite of 6, compounds 1-5 show photochromic behavior under UV excitation. Namely, compounds 1-5 shift from white or pale yellow to pale pink, reddish brown, or purple under UV illumination depending on the chemical nature of the mineral framework, with the kinetics of the color change being dictated by the nature of the organic component and by the organic-inorganic interface.     

Framework fluxionality of organometallic oxides: synthesis, crystal structure, EXAFS, and DFT studies on [[Ru(eta6-arene)]4Mo4O16] complexes

Reactions of the molybdates Na(2)MoO4.2 H2O and (nBu(4)N)2[Mo2O7] with [[Ru(arene)Cl(2)](2)] (arene=C(6)H5CH3, 1,3,5-C6H3(CH3)(3), 1,2,4,5-C6H2(CH3)4) in water or organic solvents led to formation of the triple-cubane organometallic oxides [[Ru(eta(6)-arene)](4)Mo4O16], whose crystal and molecular structures were determined. Refluxing triple cubane [[Ru(eta(6)-C6H5CH3)](4)Mo4O16] in methanol caused partial isomerization to the windmill form. The two isomers of [[Ru(eta(6)-C6H5CH3)](4)Mo4O16] were characterized by Raman and Mo K-edge X-ray absorption spectroscopy (XAS), both in the solid-state and in solution. This triple-cubane isomer was also used as a spectroscopic model to account for isomerization of the p-cymene windmill [[Ru(eta(6)-1,4-CH3C6H4CH(CH3)2)](4)Mo4O16] in solution. Using both Raman and XAS techniques, we were then able to determine the ratio between the windmill and triple-cubane isomers in dichloromethane and in chloroform. Density functional calculations on [[Ru(eta(6)-arene)](4)Mo4O16] (arene=C6H6, C6H5CH3, 1,3,5-C6H3(CH3)3, 1,4-CH3C6H4CH(CH3)2, C6(CH3)6) suggest that the windmill form is intrinsically more stable, provided the complexes are assumed to be isolated. Intramolecular electrostatic interactions and steric bulk induced by substituted arenes were found to modulate but not to reverse the energy difference between the isomers. The stability of the triple-cubane isomers should therefore be accounted for by effects of the surroundings that induce a shift in the energy balance between both forms.     

Complexation of molybdenum(V) with glycolic acid: an unusual orientation of glycolato ligand in {Mo2O4}2+ complexes

(PyH)5[Mo(V)OCl4(H2O)]3Cl2 and (PyH)n[Mo(V)OBr4]n reacted with glycolic acid (H2glyc) or its half-neutralized ion (Hglyc(-)) to afford a series of novel glycolato complexes based on the {Mo(V)2O4}2+ structural core: (PyH)3[Mo2O4Cl4(Hglyc)]. (1)/ 2CH 3CN (1), (PyH) 3[Mo 2O 4Br 4(Hglyc)].Pr(i)OH(2), (PyH)2[Mo2O4(glyc) 2Py 2] (3), (PyH) 4[Mo 4O 8Cl 4(glyc) 2].2EtOH (4), and [Mo 4O 8(glyc) 2Py 4] (5) (Py = pyridine, C 5H 5N; PyH(+) = pyridinium cation, C 5H 5NH (+) and glyc (2-) = a doubly ionized glycolate, (-)OCH 2COO (-)). The compounds were fully characterized by X-ray crystallography and infrared spectroscopy. The Hglyc (-) ion binds to the {Mo 2O 4} (2+) core through a carboxylate end in a bidentate bridging manner, whereas the glyc (2-) ion adopts a chelating bidentate coordination through a deprotonated hydroxyl group and a monodentate carboxylate. The orientations of glyc (2-) ions in 3- 5 are such that the alkoxyl oxygen atoms occupy the sites opposite the multiply bonded oxides. {(C6H5) 4P}[Mo(VI)O 2(glyc)(Hglyc)] ( 6), an oxidized complex, features a reversed orientation of the glyc(2-) ion. The theoretical DFT calculations on the [Mo(V)2O4(glyc) 2Py 2](2-) and [Mo(VI)O2(glyc)2](2-) ions confirm that binding of glycolate with the alkoxyl oxygen to the site opposite the MoO bond is energetically more favorable in {Mo(V)2O4}(2+) species, whereas a reversed orientation of the ligand is preferred in Mo(VI) complexes. An explanation based on the orbital analysis is put forward.     

[C6N2H18]2[Mo5O15(HPO4)2]·H2O的水热合成与结构表征

通过水热法合成了一个新化合物[C6N2H18]2[Mo5O15(HPO4)2]·H2O,并通过IR光谱、ICP、元素分析、差热与热重分析和X射线单晶衍射分析等手段进行了表征.结果表明,晶体属三方晶系,P3(2)21空间群,a=1.1231(1)nm,c=2.2802(5)nm,V=2.4911(7)nm3,Dx=2.835Mg/m3,Z=6,最后的一致性因子R=0.0227,wR=0.0675.阴离子中Mo5O15构成一环状结构,2个HPO4一个连在环的下方,一个连在环的上方,形成类似于“飞碟”状的结构,阳离子为2个质子化的四甲基乙二胺.     

Solid-state coordination chemistry: influences of (M(terpyridyl))(M = Fe(III), Cu(II), Ni(II)) subunits on molybdenum oxide structures

The hydrothermal reactions of Na2MoO4 x 2H2O and 2,2':6',2"-terpyridine with appropriate salts of Fe(II), Cu(II), and Zn(II) yield a variety of mixed metal oxide phases. The Cu(II) system affords the molecular cluster [Cu(terpy)MoO4].3H2O (MOXI-40 x 3H2O), as well as a one-dimensional material [Cu(terpy)Mo2O7](MOXI-41) which is constructed from (Mo4O14)4- clusters linked through (Cu(terpy))2+ units. In constrast, the Zn(II) phase of stoichiometry identical to that of MOXI-41, [Zn(terpy)Mo2O7](MOXI-42), exhibits a one-dimensional structure characterized by a (Mo2O7)n2n- chain decorated with peripheral (Zn(terpy))2+ subunits. The iron species [(Fe(terpy))2Mo4O12](MOXI-43) is also one-dimensional but exhibits [(Fe(terpy))2(MoO4)2]2+ rings linked through (MoO4)2- tetrahedra. A persistent structural motif which appears in MOXI-40, MOXI-41, and MOXI-43 is the [(M(terpy))2(MoO4)2]n cluster with a cyclic )(M2Mo2O4) core. In general, the secondary metal sites M(II, III) are effective bridging groups between molybdate subunits of varying degrees of aggregation. Furthermore, the ligands passivate the bimetallic oxide from spatial extension in two or three dimensions and provide a routine entree into low-dimensional structural types of the molybdenum oxide family of materials.     

An octanuclear molybdenum(VI) complex containing coordinatively bound 4,4'-di-tert-butyl-2,2'-bipyridine, [Mo8O22(OH)4(di-tBu-bipy)4]: synthesis, structure, and catalytic epoxidation of bio-derived olefins

The reaction of [MoO(2)Cl(2)(di-tBu-bipy)] (1) (di-tBu-bipy = 4,4'-di-tert-butyl-2,2'-bipyridine) with water at 100-120 °C in a Teflon-lined stainless steel autoclave, in an open reflux system, or in a microwave synthesis system gave the octanuclear complex [Mo(8)O(22)(OH)(4)(di-tBu-bipy)(4)] (2) as a microcrystalline powder in good yields. Single crystals of 2 suitable for X-ray diffraction were obtained by the reaction of MoO(3) and di-tBu-bipy in water at 160 °C for 3 days. The molecular structure of 2 comprises a purely inorganic core, Mo(4)O(8)(μ(3)-OH)(2)(μ(2)-O)(2), attached to two peripheral oxo-bridged binuclear units, Mo(2)O(4)(μ(2)-O)(2)(OH)(di-tBu-bipy)(2). The inorganic core is composed of a unique assembly of four {MoO(5)} distorted square pyramids connected to each other via edge-sharing. Overall, the octanuclear complex adopts a highly distorted form strongly resembling an "S"-shaped molecular unit. Complex 2 was applied in the catalytic epoxidation of the biorenewable olefins DL-limonene (Lim) and methyl oleate (Ole), using tert-butylhydroperoxide (TBHP) as an oxygen donor, under mild reaction conditions (55 °C, air). The reactions of Lim and Ole gave the respective epoxide monomers in fairly high selectivities at high conversions (89% 1,2-epoxy-p-menth-8-ene selectivity at 96% Lim conversion; 99% methyl 9,10-epoxystearate selectivity at 94% Ole conversion, reached within 24 h reaction). Iodometric titrations revealed no measurable "non-productive" decomposition of TBHP.     

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.