Dimeric dioxomolybdenum(VI) and oxomolybdenum(V) complexes with citrate at very low pH and neutral conditions

A novel dimeric dioxomolybdenum(VI) citrate complex, K[(MoO2)2-(OH)(H2cit)2].4H2O (1), with weak coordination of beta-carboxylic acid groups and the first structural example of an oxomolybdenum(V) citrate complex, (NH4)6[Mo2O4(cit)2].3H2O (2) (H4cit = citric acid), are isolated in a very acidic solution (pH 0.5-1.0) and neutral conditions (pH 7.0-8.0), respectively. Complex 1 displays strong double hydrogen bonds through beta-carboxyl and beta-carboxylic acid groups [2.621(9) A]. Transformations of the dimeric molybdenum(VI) citrate show that protonation of a carboxyl group will weaken the coordination of molybdenum(VI) citrate. There are obvious dissociations of molybdenum(VI/V) citrate complexes based on 13C NMR observations in solution.     

Syntheses and spectroscopic and structural characterization of molybdenum(VI) citrato monomeric raceme and dimer, K4[MoO3(cit)].2H2O and K4[(MoO2)2O(Hcit)2].4H2O

Investigation of the aqueous coordination chemistry for citrate and molybdenum(VI) resulted in the isolation of molybdenum(VI) citrato monomeric raceme and dimer K4[MoO3(cit)].2H2O (1) and K4[(MoO2)2O(Hcit)2].4H2O (2) (H4cit = citric acid). Complex 1 can serve as the first structurally characterized monomeric citrato molybdate and may represent an early mobilized precursor in the biosynthesis of FeMo-co (FeMo-cofactor). The two complexes have been characterized by elemental analyses and IR and NMR spectroscopies. The IR and NMR spectra are consistent with a monomeric species or a monooxo-bridged dinuclear structure, as revealed by a single crystal X-ray diffraction study. Compound 1 is monoclinic space group P2(1)/c with a = 7.225(1) A, b = 9.151(2) A, c = 22.727(2) A, beta = 94.93(1) degrees, V = 1497.1(7) A3, and Z = 4. Full-matrix least-squares refinement resulted in residuals of R = 0.027 and Rw = 0.032. The molybdenum atom forms an octahedral coordination with three oxo groups and one tridentate citrate, in which the latter is coordinated through the alkoxy and vicinal carboxyl and much more weakly by one of the two terminal groups [2.411(3) A]. Compound 2 is triclinic space group P1 with a = 8.2728(8) A, b = 8.9514(8) A, c = 10.0605(9) A, alpha = 101.673(8) degrees, beta = 100.672(7) degrees, gamma = 112.938(7) degrees, V = 642.5(3) A3, and Z = 1. Full-matrix least-squares refinement resulted in residuals of R = 0.033 and Rw = 0.039. The complex anion contains a linear (O2Mo)O(MoO2) core with the bridging oxo group lying at the center of inversion symmetry (Mo-Ob-Mo, 180 degrees). Each citrate ligand is three-coordinated to one molybdenum atom through the deprotonated hydroxy, alpha-carboxyl, and one beta-carboxyl group, making each metal atom six-coordinate.     

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.     

Syntheses, spectroscopies and structures of molybdenum(VI) complexes with homocitrate

Initial investigations into the possible role of homocitric acid in iron molybdenum cofactor (FeMo-co) of nitrogenase lead us to isolate and characterize two tetrameric molybdate(VI) species. The complexes K2(NH4)2[(MoO2)4O3(R,S-Hhomocit)2].6H2O (1) and K5[(MoO2)4O3(R,S-Hhomocit)2]Cl.5H2O (2) (homocitric acid = H4homocit, C7H10O7) are prepared from the reactions of acyclic homocitric acid and molybdates, which represent the first synthetic structural examples of molybdenum homocitrate complexes. The homocitrate ligand trapped by tetranuclear molybdate coordinates to the molybdenum(VI) atom through alpha-alkoxy and alpha-, beta-carboxy groups. The physical properties, structural parameters, and their possible biological relevances are discussed.     

Formations of mixed-valence oxovanadiumV,IV citrates and homocitrate with N-heterocycle chelated ligand

Dimeric mixed-valence oxovanadium citrate [V 2O 3(phen) 3(Hcit)].5H 2O ( 1) (H 4cit = citric acid, phen = 1,10-phenanthroline) was isolated from a weak acidic medium. It could be converted quantitatively into a tetrameric oxovanadium citrate adduct of 1,10-phenanthroline [V 2O 3(phen) 3(Hcit) 2(phen) 3O 3V 2].12H 2O ( 2). This was supported by the trace of infrared spectra and X-ray diffraction patterns. The two compounds feature a bidentate citrate group that chelates only to one vanadium center through their negatively charged alpha-alkoxy and alpha-carboxy oxygen atoms, while the other beta-carboxy and beta-carboxylic acid groups are free to participate in strong intramolecular and intermolecular hydrogen bonding [2.45(1) in 1 and 2.487(2) A in 2], respectively. This is also the case of homocitrato vanadate(V/IV) [V 2O 3(phen) 3( R, S-H 2homocit)]Cl.6H 2O ( 3) (H 4homocit = homocitric acid), which features a binding mode similar to that found in the R-homocitrato iron molybdenum cofactor of Mo-nitrogenase. Moreover, the homocitrato vanadate(V) [VO 2(phen) 2] 2[V 2O 4( R,S-H 2homocit) 2].4H 2O.2C 2H 5OH ( 4) is isolated as a molecular precursor for the formation of mixed-valence complex 3. The V-O alpha-alkoxy and V-O alpha-carboxy bond distances of homocitrate complexes 3 and 4 are 1.858(4) and 1.968(6) av and 2.085(4) and 1.937(5) A, respectively. They are shorter than those of homocitrate to FeVco (2.15 A). The gamma-carboxy groups of coordinated homocitrato complexes 3 and 4, and the free homocitrate salt Na 3(Hhomocit).H 2O ( 5), form strong hydrogen bonds with the chloride ion and the water molecule [2.982(5) in 3, 2.562(9) in 4, and 2.763(1) A in 5], respectively.     

Solid and Solution Structural Studies of Dimeric and Tetrameric Molybdenum（VI） Malate Complexes

Reactions of potassium molybdate with racemic malic acid （H3mal = C4H6O5） result in the isolation of two mesomeric molybdenum malate complexes K8[（MoO2）2O（R-mal）2][（MoO2）2O（Smal）2]-4H2O 1 and （Him）2K6[（MoO2）4O3（R-mal）2][（MoOE）4O3（S-mal）2]-8H2O 2. Complex 1 belongs to the monoclinic system, space group C2/c with a = 14.8637（3）, b = 6.9544（1）, c = 19.6783（5）A, β = 100.081（2）°, V = 2002.70（7） A^3, Mr = 1452.88, Z = 2, F（000） = 1416, T = 173 K, Dc = 2.409 g/cm3, fl（MoKa＇） = 2.167, R = 0.0283 and wR = 0.0733.2 is of triclinic system, space group P1^- with a = 8.7707（2）, b = 9.3310（3）, c = 17.9093（7）A, α= 83.781（3）, β = 85.626（2）, y= 84.822（2）°, V = 1447.84（8）A^3, Mr = 2160.68, Z = 1, F（000） = 1048, T = 173 K, Dc = 2.478 g/cm^3,μ（MoKα） = 2.230, R = 0.0234 and wR = 0.0584.1 is the first isolated dinuclear molybdenum（VI） malato complex in 1：1 molar ratio. The molybdenum atoms in the two complexes are six-coordinated in an approximately octahedral geometry. Two malates coordinate tridentately with the Mo atom via their α-alkoxy, α-carboxy and α-carboxy groups in 1 and 2. β-Carboxy group in 2 further links with the other two Mo atoms to give a tetrameric unit. The solution ^1H and ^13C NMR spectra indicate that dimeric malate molybdenum in 1 dissociates partly in solution and exists in an equilibrium with tetrameric species, while 2 is stable and retains its tetrameric structure without any dissociation.     

Asymmetric dinuclear hydroxyl and ethoxyl citrato dioxovanadates(V)

Asymmetric citrato dioxovanadates(V), [Hneo]₄[V₂O₄(R-Hcit)(OH)][V₂O₄(S-Hcit)(OH)]?·?4H₂O (1) and [Ni(phen)₃]₂[V₂O₄(R-Hcit)(OC₂H₅)][V₂O₄(S-Hcit)(OC₂H₅)]?·?4H₂O (2) and (H₄cit?=?citric acid, neo?=?2,9-dimethyl-1,10-phenanthroline, phen?=?1,10-phenanthroline) are isolated with the help of large counterions. Structural analyses of complexes 1 and 2 show that vanadium atoms are coordinated by tridentate citrate ligand and hydroxy or ethoxy groups, respectively. The insertions of hydroxy and ethoxy groups give new examples of the mixed RO-bridges for vanadium–citrate complexes.     

Solid and Solution Structural Studies of Dimeric and Tetrameric Molybdenum(Ⅵ) Malate Complexes

Reactions of potassium molybdate with racemic malic acid (H3mal = C4H6O5) result in the isolation of two mesomeric molybdenum malate complexes Ks[(MoO2)2O(R-mal)2][(MoO2)2O(S- mal)2]·4H2O 1 and (Him)2K6[(MoO2)4O3(R-mal)2][(MoO2)4O3(S-mal)2]·8H2O 2. Complex 1 belongs to the monoclinic system, space group C2/c with a = 14.8637(3), b = 6.9544(1), c = 19.6783(5) A, β = 100.081(2)°, V= 2002.70(7)A3, Mr = 1452.88, Z= 2, F(000) = 1416, T= 173 K, Dc = 2.409 g/cm3, μ(MoKa) = 2.167, R = 0.0283 and wR = 0.0733.2 is of triclinic system, space group P1 with a = 8.7707(2), b = 9.3310(3), c = 17.9093(7) A, α = 83.781(3), β = 85.626(2), γ= 84.822(2)°, V = 1447.84(8) A3, Mr = 2160.68, Z = 1, F(000) = 1048, T= 173 K, Dc = 2.478 g/cm3, μ(MoKα) = 2.230, R = 0.0234 and wR = 0.0584.1 is the first isolated dinuclear molybdenum(Ⅵ) malato complex in 1:1 molar ratio. The molybdenum atoms in the two complexes are six-coordinated in an approximately octahedral geometry. Two malates coordinate tridentately with the Mo atom via their α-alkoxy, α-carboxy and α-carboxy groups in 1 and 2. β-Carboxy group in 2 further links with the other two Mo atoms to give a tetrameric unit. The solution 1H and 13C NMR spectra indicate that dimeric malate molybdenum in 1 dissociates partly in solution and exists in an equilibrium with tetrameric species, while 2 is stable and retains its tetrameric structure without any dissociation.     

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.     

pH-dependent isolations and spectroscopic, structural, and thermal studies of titanium citrate complexes

Titanium(IV) citrate complexes (NH(4))(2)[Ti(H(2)cit)(3)].3H(2)O (1), (NH(4))(5)[Fe(H(2)O)(6)][Ti(H(2)cit)(3)(Hcit)(3)Ti].3H(2)O (2), Ba(2)[Ti(H(2)cit)(Hcit)(2)].8H(2)O (3), and Ba(3)(NH(4))(7)[Ti(cit)(3)H(3)(cit)(3)Ti].15H(2)O (4) (H(4)cit = citric acid) were isolated in pure form from the solutions of titanium(IV) citrate with various countercations. The isolated complexes were characterized by elemental analyses, IR spectra, and (1)H NMR and (13)C NMR spectra. The formation of titanium(IV) citrate complexes depends mainly on the pH of the solutions, that is, pH 1.0-2.8 for the formation of ammonium titanium(IV) citrate 1, pH 2.5-3.5 for ammonium iron titanium(IV) citrate 2, pH 2.8-4.0 for dibarium titanium(IV) citrate 3, and pH 5.0-6.0 for ammonium barium titanium(IV) citrate 4. X-ray structural analyses revealed that complexes 2-4 featured three different protonated forms of bidentate citrate anions that chelate to the titanium(IV) atom through their negatively charged alpha-alkoxyl and alpha-carboxyl oxygen atoms. This is consistent with the large downfield shifts of the (13)C NMR spectra for the carbon atoms bearing the alpha-alkoxyl and alpha-carboxyl groups. The typical coordination modes of the barium atoms in complexes 3 and 4 are six-coordinated, with three alpha-alkoxyl groups and three beta-carboxyl groups of citrate ions. The strong hydrogen bonding between the beta-carboxylic acid and the beta-carboxyl groups [2.634(8) A for complex 2, 2.464(7) A for complex 3, and 2.467(7) A for complex 4] may be the key factor for the stabilization of the citrate complexes. The decomposition of complex 3 results in the formation of a pure dibarium titanate phase and 4 for the mixed phases of dibarium titanate and barium titanate at 1000 degrees C.     

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.     

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.     

Mechanochemical and solution synthesis, and crystal structures and IR and solid-state (CPMAS) NMR spectroscopy of some bis(triphenylphosphine)silver(I) mono- and di-hydrogencitrate systems

The complex [(Ph(3)P)(2)Ag(H(2)cit)]·EtOH (1; H(2)cit(-) = dihydrogencitrate = C(6)H(7)O(7)(-)) contains [(Ph(3)P)(2)Ag(H(2)cit)] molecules in which the silver atom is coordinated to two PPh(3) molecules and the two oxygen atoms of one of the 'terminal'/1-carboxylate groups of the dihydrogencitrate group. The molecules form centrosymmetric hydrogen-bonded dimers in the solid. In [{(Ph(3)P)(2)Ag}(2)(Hcit)], (2), unsymmetrical deprotonation of the citrate grouping is found, from the 1- and 3- (i.e. terminal and central) carboxylates: [(Ph(3)P)(2)Ag(O(2)CCH(2)C(OH) (CH(2)COOH)CO(2))Ag(PPh(3))(2)]. The above complexes, as well as [(Ph(3)P)(3)Ag(H(2)cit)] (3) were prepared via conventional solution methods, involving the reaction of trisilver(I) citrate, citric acid and triphenylphosphine, and by a mechanochemical method involving the reaction of silver(I) oxide, citric acid and triphenylphosphine. IR studies of 1-3 show the presence of coordinated carboxylate and free carboxylic acid groups in the mono- and di-hydrogencitrate ligands, and the formation of 2 from 1 shows that dihydrogencitrate deprotonation can occur upon dissolution of 1 in protic solvents. High-field (9.40 T) (31)P CPMAS NMR spectra were recorded and analysed, yielding heteronuclear (1)J((107/109)Ag,(31)P) and homonuclear (2)J((31)P,(31)P) spin-spin coupling constants.     

The hydrothermal syntheses and characterization of one- and two-dimensional structures constructed from metal-organic derivatives of polyoxometalates: [(Cu(bpy)2)(Cu(bpy)(H2O))(Mo5O15)(O3P(CH2)4PO3)].H2O and [(u2(tpypyz)(H2O)2)(Mo5O15)(O3PCH2CH2PO3)].5.5H2O [bpy = 2,2'-bipyridine,tpypyz = tetra(2-pyridyl)pyrazine

The hydrothermal reaction of CuSO(4).5H2O, Na2MoO(4).2H2O and 2,2'-bipyridine with the bridging diphosphonate ligand H2O3P(CH2)4PO3H2 yields the one-dimensional chain [(Cu(bpy)2)(Cu(bpy)(H2O)2)(Mo5O15)(O3P(CH2)4PO3)].H2O; the introduction of a second bridging component in the reaction of Cu(MeCO2)2.H2O, MoO3, H2O3PCH2CH2PO3H2 and tetra(2-pyridyl)pyrazine yields the network solid [(Cu2(tpypyz)(H2O)2)(Mo5O15)(O3PCH2CH2PO3)].5.5H2O.     

Synthesis and properties of mononuclear and binuclear molybdenum complexes derived from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

The monomer molybdenum(VI) complex [MoO(2)(napoxlhH(2))].2H(2)O (1) has been synthesized from the reaction of MoO(2)(acac)(2) with bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (napoxlhH(4)) in 1:1 molar ratio in ethanol under reflux. This complex on reaction with pyridine/3-picoline/4-picoline yielded the dimer molybdenum(VI) complexes [Mo(2)O(4)(napoxlhH(2))(2)(A)(2)].2H(2)O (A=py (2), 3-pic (3), 4-pic (4)), whereas reaction with isonicotinoylhydrazine (inhH(3)) and salicyloylhydrazine (sylshH(3)) lead to the reduction of the metal centre yielding monomeric molybdenum(V) complexes [Mo(napoxlhH(2))(hzid)].2H(2)O (where hzidH(3)=inhH(3) (5) and sylshH(3) (6)). The complexes have been characterized by elemental analyses, molecular weight determinations, molar conductance data, magnetic moment data, electronic, IR, ESR and (1)H NMR spectroscopic studies. The complexes (5) and (6) are paramagnetic to the extent of one unpaired electron. The electronic spectra of the complexes are dominated by strong charge transfer bands. In all of the complexes, the principal dihydrazone ligand has been suggested to coordinate to the metal centres in the anti-cis-configuration. The complexes (1), (5) and (6) are suggested to have six-coordinate octahedral stereochemistry around molybdenum(VI) and molybdenum(V) metal centres, respectively, while the complexes (2)-(4) are suggested to have eight coordinate dodecahedral stereochemistry around molybdenum(VI) metal centre.     

Formation and reactivity of the Os(IV)-azidoimido complex, PPN[Os(IV)(bpy)(Cl)(3)(N(4))

Reactions between the Os(VI)-nitrido complexes, [OsVI(L2)(Cl)3(N)] (L2 = 2,2'-bipyridine (bpy) ([1]), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 1,10-phenanthroline (phen), and 4,7-diphenyl-1,10-phenanthroline (Ph2phen)), and bis-(triphenylphosphoranylidene)ammonium azide (PPNN3) in dry CH3CN at 60 degrees C under N2 give the corresponding Os(IV)-azidoimido complexes, [OsIV(L2)(Cl)3(NN3)]- (L2 = bpy = [2]-, L2 = Me2bpy = [3]-, L2 = phen = [4]-, and L2 = Ph2phen = [5]-) as their PPN+ salts. The formulation of the N42- ligand has been substantiated by 15N-labeling, IR, and 15N NMR measurements. Hydroxylation of [2]- at Nalpha with O<--NMe3.3H2O occurs to give the Os(IV)-azidohydroxoamido complex, [OsIV(bpy)(Cl)3(N(OH)N3)] ([6]), which, when deprotonated, undergoes dinitrogen elimination to give the Os(II)-dinitrogen oxide complex, [OsII(bpy)(Cl)3(N2O)]- ([7]-). They are the first well-characterized examples of each kind of complex for Os.     

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.     

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.     

A new modification of an old framework: Hofmann layers with unusual tetracyanidometallate groups

Cyanidometallate complexes are highly versatile building units for the generation of functional porous materials. Here we report five new pillared Hofmann layer compounds incorporating the tetracyanidometallates [MoO(CN)(4)](2-) and [MnN(CN)(4)](2-). These metalloligands, which are new to this class of materials, have been combined with divalent 1st-row transition metals to produce Hofmann layers that are linked into three-dimensional frameworks by ditopic bridging dipyridyls. We report the structures and anomalous thermal expansion properties of five new materials: [Mn(H(2)O)(bpy)(?){MoO(CN)(4)(bpy)(?)}]·2H(2)O (1), [Mn(H(2)O)(bpy)(?){MnN(CN)(4)(bpy)(?)}]·2H(2)O (2), [Fe(H(2)O)(bpy)(?){MnN(CN)(4)(bpy)(?)}]·2H(2)O (3), [Co(H(2)O)(bpy)(?){MnN(CN)(4)(bpy)(?)}]·2H(2)O (4) and [{Mn(H(2)O)(2)}(?){Mn(bpa)(2)}(?){MoO(CN)(4)(bpa)(?)}]·MeOH (5), (where bpy = 4,4'-bipyridine and bpa = 4,4'-bipyridylacetylene).     

Spontaneously organizing metal connectors as supramolecular structure directors of two- and three-dimensional organometallic assemblies

The supramolecular interplay of Me(3)Sn(+) and [M(CN)(2n)](n-) ions (n=3 and 4) with either 4,4'-bipyridine (bpy), trans-bis(4-pyridyl)ethene (bpe) or 4cyanopyridine (cpy) in the presence of H(2)O has been investigated for the first time. Crystal structures of the six novel assemblies: [(Me(3)Sn)(4)Mo(IV)(CN)(8).2 H(2)O.bpy] (8) and [(Me(3)Sn)(4)Mo(IV)(CN)(8).2 H(2)O.bpe] (8 a; isostructural), [(Me(3)Sn)(3)Fe(III)(CN)(6).4 H(2)O.bpy] (9), [(Me(3)Sn)(3)Co(III)(CN)(6).3 H(2)O.3/2 bpy] (10), [(Me(3)Sn)(4)Fe(II)(CN)(6).H(2)O.3/2 bpy] (11), and [(Me(3)Sn)(4)Ru(II)(CN)(6).2 H(2)O.3/2 cpy] (12) are presented. H(2)O molecules are usually coordinated to tin atoms and involved in two significant O-H.N hydrogen bonds, wherein the nitrogen atoms belong either to bpy (bpe, cpy) molecules or to M-coordinated cyanide ligands. Extended supramolecular assemblies such as -CN-->Sn(Me(3))<--O(H.)H.N(L)N.HO(H.)-->Sn(Me(3))<--NC- (L=bpy, bpe or cpy) function as efficient metal connectors (or spacers) in the structures of all six compounds. Only in the three-dimensional framework of 11, one third of all bpy molecules is involved in coordinative N-->Sn bonds. The supramolecular architecture of 9 involves virtually non-anchored (to cyanide N atoms), Me(3)Sn(+) units with a strictly planar SnC(3) skeleton, and two zeolitic H(2)O molecules. Pyrazine (pyz) is surprisingly reluctant to afford assemblies similar to 8-12, however, the genuine host-guest systems [(Me(3)Sn)(4)Mo(CN)(8).0.5pyz] and [(Me(3)Sn)(4)Mo(CN)(8).pym] (pym=pyrimidine) could be isolated and also structurally characterized.