Structural analysis and characterization of layer perovskite oxynitrides made from Dion-Jacobson oxide precursors

A three-layer oxynitride Ruddlesden-Popper phase Rb_1+xCa₂Nb₃O_10−xN_x·yH₂O (x=0.7-0.8, y=0.4-0.6) was synthesized by ammonialysis at 800 °C from the Dion-Jacobson phase RbCa₂Nb₃O₁₀ in the presence of Rb₂CO₃. Incorporation of nitrogen into the layer perovskite structure was confirmed by XPS, combustion analysis, and MAS NMR. The water content was determined by thermal gravimetric analysis and the rubidium content by ICP-MS. A similar layered perovskite interconversion occurred in the two-layer Dion-Jacobson oxide RbLaNb₂O₇ to yield Rb_1+xLaNb₂O_7−xN_x·yH₂O (x=0.7-0.8, y=0.5-1.0). Both compounds were air- and moisture-sensitive, with rapid loss of nitrogen by oxidation and hydrolysis reactions. The structure of the three-layer oxynitride Rb_1.7Ca₂Nb₃O_9.3N_0.7·0.5H₂O was solved in space group P4/mmm with a=3.887(3) and , by Rietveld refinement of X-ray powder diffraction data. The two-layer oxynitride structure Rb_1.8LaNb₂O_6.3N_0.7·1.0H₂O was also determined in space group P4/mmm with a=3.934(2) and . GSAS refinement of synchrotron X-ray powder diffraction data showed that the water molecules were intercalated between a double layer of Rb+ ions in both the two- and three-layer Ruddlesden-Popper structures. Optical band gaps were measured by diffuse reflectance UV-vis for both materials. An indirect band gap of 2.51 eV and a direct band gap of 2.99 eV were found for the three-layer compound, while an indirect band gap of 2.29 eV and a direct band gap of 2.84 eV were measured for the two-layer compound. Photocatalytic activity tests of the three-layer compound under 380 nm pass filtered light with AgNO₃ as a sacrificial electron acceptor gave a quantum yield of 0.025% for oxygen evolution.     

Nb-Ta, Nb-Mo and Nb-V oxides prepared from hybrid organic-inorganic precursors

New hybrid organic-inorganic materials based on group 5 elements and a well-defined polymeric matrix have been prepared and used as precursors for Nb-Ta and Nb-Mo mixed oxides. In this non-conventional but easily accessible route to multimetallic oxides, a copolymer of N,N-diallyl-N-hexylamine and maleic acid was synthesised and used as matrix to stabilise inorganic species generated in solution from (NH₄)₆Mo₇O₂₄·4H₂O, NH₄VO₃, (gu)₃[Nb(O₂)₄] and (gu)₃[Ta(O₂)₄]. Solid-state studies indicate that the homogeneity of the blends can be kept up to about 0.5 mol Nb^V and Ta^V and 0.25 mol V^V per mol of repeat units of the copolymer. The calcination conditions of these homogeneous hybrid precursors were optimised to produce Nb-Mo, Nb-Ta and Nb-V oxides. While the thermal treatment of the Nb-V hybrid blends led only to a mixture of different phases, the characterisation of the final phases by X-ray diffraction (XRD) proved the formation of pure Nb₂Mo₃O₁₄ and showed that Nb-Ta oxides could be synthesised as single phases corresponding to a continuous series of solid solutions.     

Synthesis, spectroscopic and structural characterisation of molybdenum, tungsten and manganese carbonyl complexes of tetrathio- and tetraseleno-ether ligands

A range of complexes of the binucleating tetrathio- and tetraseleno-ether ligands, 1,2,4,5-C₆H₂(CH₂EMe)₄ (E = S, L³ or Se, L⁴) or C(CH₂EMe)₄ (E = S, L⁵ or Se, L⁶) and of bidentate analogues 1,2-C₆H₂(CH₂EMe)₂ (E = S, L¹ or Se = L²) with molybdenum and tungsten carbonyls and manganese carbonyl chloride have been prepared, and characterised by IR and multinuclear NMR (¹H, ¹³C{¹H}, ⁷⁷Se, ⁵⁵Mn, ⁹⁵Mo) spectroscopy and mass spectrometry. Crystal structures are reported for [Mo(CO)₄(L²)], [Mo(CO)₄(L³)], [Mo(CO)₄(μ-L³)Mo(CO)₄], [Mo(CO)₄(L⁴)], [Mn(CO)₃Cl(μ-L³)Mn(CO)₃Cl], [Mo(CO)₄(μ-L⁵)Mo(CO)₄], [Mn(CO)₃Cl(L⁵)] and two forms (containing meso and DL diastereoisomers) of [W(CO)₄(L⁵)].     

One-step synthesis of dispersed bimetallic carbides and nitrides from transition metals hexamethylenetetramine complexes

Bimetallic nitrides and carbides Co(Ni)-Mo were obtained from the decomposition of transition metals complexes with hexamethylenetetramine (HMTA) under inert atmosphere. The precursor complexes were prepared by means of aqueous precipitation of ammonium molybdate with cobalt nitrate or nickel nitrate and HMTA. During the decomposition, HMTA acts at once as a reducing agent and as a source of carbon and nitrogen. The precursor's composition and the decomposition conditions are the key parameters to influence the nature of the obtained phases. The method developed provides a simple one-step way to highly divided bimetallic nitrides and carbides.     

Synthesis and crystal structures of cyclodiazastannoxides fused cyclopentadienyl M-Sn (M = Mo, W) bonded organometallic heterocycle

The condensation reaction of CH₃COC₅H₄M(CO)₃SnCl₃ (M = Mo or W) with PyCONHNH₂ (Py = 2,3,4-pyridyl or 2-pyridylmethyl) in mild conditions yields cyclodiazastannoxides fused cyclopentadienyl M-Sn bonded organometallic heterocycle {μ-[C₅H₄(CH₃)CN-NC(O)PyH]M(CO)₃SnCl₃}. The similar reaction of CH₃COC₅H₄M(CO)₃SnCl₃ with ArCONHNH₂ (Ar = 2-furanyl) gives complexes μ-[C₅H₄(CH₃)CN-NC(O)Ar]M(CO)₃SnCl₂(H₂O), in which the water molecule can be replaced by other N-donor ligands, such as pyridine or 4,4-bipyridine. Arene-bridged organometallic heterocyclic complexes μ-{[C₅H₄(CH₃)CN-NC(O)]₂C₆H₄}{M(CO)₃SnCl₂(Solvent)}₂ have also been prepared by the reaction of CH₃COC₅H₄M(CO)₃SnCl₃ with terephthaloyl hydrazine. In these new organometallic heterocyclic complexes, it seems that the tin atom prefers to be six-coordinate through absorbing the chloridion or solvent molecules.     

Synthesis,Structural Characterization and Preliminary Biological Studies of Several Heterocyclic Transition Metal Carbonyl Complexes

The reaction of molybdenum, tungsten and manganese carbonyls with several thiazole heterocycle ligands yielded a number of coordinated transition metal complexes 1 – 10 . Of these complexes 1 – 6 are new compounds which have not been reported to date. The structures of new compounds were characterized by FT‐IR and ¹H‐NMR spectroscopy as well as single‐crystal X‐ray diffraction analysis. Complexes 1 – 10 are carbon monoxide releasing molecules that show structure‐related anti‐cancer activity. The cytotoxicity of all compounds on Hela cells was evaluated by MTT assay, and the results show that carbon monoxide releasing molecules containing such Schiff base ligands may have biomedical applications for their anti‐tumor effect.     

Facile Synthesis of Linear and Cyclic Poly(diphenylacetylene)s by Molybdenum and Tungsten Catalysis

Improved methods for the synthesis of linear and cyclic poly(diphenylacetylene)s by polymerization of the corresponding diphenylacetylenes using MoCl₅- and WCl₄-based catalytic systems have been developed. MoCl₅ induces migratory insertion polymerization of diphenylacetylenes in the presence of arylation reagents such as Ph₄Sn and ArSnⁿBu₃ to produce cis-stereoregular linear poly(diphenylacetyelene)s with high molecular weights (number-average molar mass (M_n)=30,000–3,200,000) in good yields (up to 98 %). On the other hand, WCl₄ induces ring expansion polymerization of diphenylacetylenes in the presence of Ph₄Sn or reducing reagents to produce cis-stereoregular cyclic poly(diphenylacetylene)s with high molecular weights (M_n=20,000–250,000) in moderate to good yields (up to 90 %). Both catalytic systems are applicable to the polymerization of various diphenylacetylenes having polar functional groups such as esters that are not efficiently polymerized by conventional methods using WCl₆-Ph₄Sn and TaCl₅-ⁿBu₄Sn systems.     

Synthesis and molecular structures of dinuclear complexes with 1,2-dihydro-1,2-diphenyl-naphtho[1,8-c,d]1,2-diphosphole as a bridging ligand

A bisphosphine in which a PhP-PPh bond bridges 1,8-positions of naphthalene, 1,2-dihydro-1,2-diphenyl-naphtho[1,8-cd]-1,2-diphosphole (1), was used as a bridging ligand for the preparation of dinuclear group 6 metal complexes. Free trans-1, a more stable isomer having two phenyl groups on phosphorus centers mutually trans with respect to a naphthalene plane, was allowed to react with two equivalents of M(CO)₅(thf) (M = W, Mo, Cr) at room temperature to give dinuclear complexes (OC)₅M(μ-trans-1)M(CO)₅ (M = W (2a), Mo (2b), Cr (2c)). The preparation of the corresponding dinuclear complexes bridged by the cis isomer of 1 was also carried out starting from the free trans-1 in the following way. Mono-nuclear complexes M(trans-1)(CO)₅ (M = W (3a), Mo (3b), Cr (3c)) which had been prepared by a reaction of trans-1 with one equivalent of the corresponding M(CO)₅(thf) (M = W, Mo, Cr) complex, were heated in toluene, wherein a part of the trans-3a-c was converted to their respective cis isomer M(cis-1)(CO)₅. Each cis trans mixture of the mono-nuclear complexes 3a-c was treated with the corresponding M(CO)₅(thf) to give a cis trans mixture of the respective dinuclear complexes 2a-c. The cis isomer of the ditungsten complex 2a was isolated, and its molecular structure was confirmed by X-ray analysis, showing a shorter W?W distance of 5.1661(3) Å than that of 5.8317(2) Å in trans-2a.     

Synthesis, structure, properties, volatility, and thermal stability of molybdenum(II) and tungsten(II) complexes containing allyl, carbonyl, and pyrazolate or amidinate ligands

Treatment of M(allyl)(Cl)(CO)₂(py)₂ (M = Mo, W) with 1 equiv. of potassium pyrazolates in tetrahydrofuran at −78 °C afforded M(allyl)(R₂pz)(CO)₂(py)_n (R₂pz = 3,5-disubstituted pyrazolate; n = 1, 2) in 68-81% yields. X-ray crystal structure analyses of Mo(allyl)((CF₃)₂pz)(CO)₂(py)₂ and W(allyl)(tBu₂pz)(CO)₂(py) revealed η¹- and η²-coordination of the (CF₃)₂pz and tBu₂pz ligands, respectively. Analogous treatment of Mo(allyl)(Cl)(CO)₂(NCCH₃)₂ with 1 equiv. of tBu₂pzK in tetrahydrofuran at −78 °C afforded [Mo(allyl)(tBu₂pz)(CO)₂]₂ in 79% yield. An X-ray crystal structure analysis of [Mo(allyl)(tBu₂pz)(CO)₂]₂ showed a dimeric structure bridged by two μ-η²:η¹-tBu₂pz ligands. Treatment of M(allyl)(Cl)(CO)₂(py)₂ with 1 equiv. of lithium 1,3-diisopropylacetamidinate or lithium 1,3-di-tert-butylacetamidinate in diethyl ether at −78 °C afforded M(allyl)(iPrNC(Me)NiPr)(CO)₂(py) and M(allyl)(tBuNC(Me)NtBu)(CO)₂(py), respectively, in 68-78% yields. The new complexes were characterized by spectral and analytical methods and by X-ray crystal structure determinations. M(allyl)(iPrNC(Me)NiPr)(CO)₂(py) adopt pseudo-octahedral geometry about the metal centers, with the 1,3-diisopropylacetamidate ligand nitrogen atoms spanning one axial site and one equatorial site of the octahedron. By contrast, M(allyl)(tBuNC(Me)NtBu)(CO)₂(py) adopt pseudo-octahedral structures in which the two 1,3-di-tert-butylacetamidinate ligand nitrogen atoms span two equatorial coordination sites. Sublimation of M(allyl)(tBuNC(Me)NtBu)-(CO)₂(py) at 105 °C/0.03 Torr afforded ?7% yields of M(allyl)(tBuNC(Me)NtBu)(CO)₂, along with sublimed M(allyl)(tBuNC(Me)NtBu)(CO)₂(py). W(allyl)(tBuNC(Me)NtBu)(CO)₂ exists in the solid state as a 16-electron complex with distorted square pyramidal geometry. Many of the new complexes undergo dynamic ligand site exchange in solution, and these processes were probed by variable temperature ¹H NMR spectroscopy. The volatilities and thermal stabilities were evaluated to determine the potential of the new complexes for use as precursors in thin film growth experiments.     

Synthesis,Crystal Structure,and Luminescence of Metal Iodide Cluster Compounds (nBu4N)2[M6I8(NCO)6] with M = Mo,W

Molybdenum and tungsten iodide clusters with the [M₆I₈] cluster core show versatile photophysical properties that strongly depend on the nature of six apical ligands (L) in [M₆I₈L₆]^2–. In course of our syntheses we report a new efficient preparation of Cs₂[Mo₆I₁₄] as precursor. Target compounds (ⁿBu₄N)₂[M₆I₈(NCO)₆] with M = Mo, W with cyanate ligands were synthesized and structurally characterized to study their photophysical properties. (ⁿBu₄N)₂[M₆I₈(NCO)₆] compounds appear as deep red (Mo) and light yellow (W) crystal powders showing strong phosphorescence. Compared to other cluster compounds of this type there is no significant concentration quenching obtained by the presence of molecular oxygen.     

Synthesis and ROMP activity of aminophenol-substituted tungsten(VI) and molybdenum(VI) complexes

Tungsten(VI) and molybdenum(VI) complexes [MO(L¹)Cl₂] and [M(X)(L²)Cl₃] (X = O, NPh) with tridentate aminobis(phenolate) ligand L¹ = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) and bidentate aminophenolate ligand L² = 2,4-di-tert-butyl-6-((dimethylamino)methyl)phenolate) were prepared and characterised. These complexes are principally stable in open atmosphere under ambient conditions. When activated with Et₂AlCl, they exhibited high activity in ring-opening metathesis polymerisation (ROMP) of 2-norbornene (NBE) and its derivatives. Especially complexes [M(NPh)(L²)Cl₃], which are easily available from corresponding metal oxides MO₃ by a simple three-step synthesis, were found very efficient ROMP catalysts for NBE (M = Mo, W) and 2-norbornen-5-yl acetate (M = Mo).     

Photodecomposition of molybdenum(II) and tungsten(II) carbonyl complexes with triazole, benz-imidazole, and oxadiazole acetylinic derivatives

Photodecomposition of 10 different molybdenum and tungsten mixed carbonyl complexes, [M(CO)₃(B)(A)]I₂ where B=o-phenanthroline or bipyridyl, A=3-(2-propynyl)thio-4,5-diphenyl-4H-1,2,4-triazole (TRZA) or S-propynyl-2-thio benz-imidazole (BIMDA) and 2(2-propynyl-thio(5-phenyl)-1,3,4-oxadiazole (OXA). M(CO)₃(TRZA)I₂, [M(CO)₂(PPh₃)_X(TRZA)I_Y]I_Z where M=Mo, X, Y and Z=1 and M=W, X and Z=2, Y=0, have been performed at 365 nm in oxygen saturated chloroform at 25 °C. The absorbance spectrum of these complexes have been recorded with the time of irradiation in order to examine the kinetics of photodecay.

The apparent rate constant (K_d) for the first-order reaction have been calculated and found to be (3.32–4.79)×10⁻⁵ s⁻¹. The primary quantum yields (Φ) has also been calculated and were in the range (8.33–12.1)×10⁻⁴. The mechanism of the photodecomposition has been suggested according to the kinetic, and photoproduct analysis data, and is similar to reaction of photo-oxidative degradation of polluted molecules in the water.     

Unique Rearrangement of an Oxycarbyne Complex: Synthesis and Structure of Novel Diborane(4)yl Complexes

Nucleophilic attack of a carbonyl oxygen atom of the complexes K[(η⁵-C₅H₅)M(CO)₃] (M=Mo, W) on each boron center gave the oxycarbyne complexes 1 . These novel products undergo a unique type of rearrangement with quantitative formation of the diborane(4)yl complexes 2 . Complex 2 (M=Mo) is the first structurally characterized boryl complex with a Mo–B bond (see structure).     

Synthesis of new diverse macrocycles from diol precursors

The formation of a library of diverse macrocycles with different ring sizes from two easily accessible building blocks is presented. Reacting diol precursors with electrophilic reagents lead to 17-membered sulfites and 19-membered malonates in 34-79% yield. Double-reductive amination of dialdehyde analogs of the diol precursors leads to 15-membered amines in yields ranging from 9 to 60%, reflecting large differences in reactivity based on steric environment.     

Pt2Mo3N and PdPtMo3N: new interstitial nitrides prepared from freeze-dried precursors

The molybdenum bimetallic and trimetallic nitrides Pt₂Mo₃N and PdPtMo₃N have been synthesized by ammonolysis of the stoichiometric amorphous precursor, obtained by freeze drying of aqueous solutions of the appropriate metal salts. These compounds have been characterized by elemental analysis, energy-dispersive analysis of X-rays, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetry analysis under an oxygen atmosphere. Pt₂Mo₃N and PdPtMo₃N crystallize in the cubic space group P4₁32 (213), with lattice parameters of a=6.83586(4) and 6.82542(3) Å, respectively, and form with the unusual filled β-manganese structure. These compounds are stable under air up to 580 K, the oxidation being complete at 910 K.     

Influence of Coordination Geometry on the Ring Opening of Benzoxazine: Oxidovanadium(V), Dioxidomolybdenum(VI) and Dioxidotungsten(VI) Complexes of Benzoxazine Based Ligands and their Bio Inspired Catalytic Applications

Mono benzoxazine appended N-capped amino bis(disubstitutedphenol) ligands [ II ( a–c )] upon reaction with V^VO(OEt)₃ in a 1 : 1 molar ratio in EtOH/MeOH give [{V^VO}en(3,5-dtbb)₃] ( 1 ), [{V^VO}en(3-tb,5-mb)₃] ( 2 ) and [{V^VO}en(3,5-dmb)₃] ( 3 ). During the reaction, the benzoxazine ring opens with the loss of methylene group and the newly formed ligands, N,N-bis(2-hydroxy-3,5-disubstitutedbenzyl)-N’-2-hydroxy-3,5-disubstituted benzyledene-1,2-diaminoethane [ III ( a–c )], behave as tribasic pentadentate in these complexes. Under similar conditions, when [M^VIO₂(acac)₂] (M=Mo or W; Hacac=acetylacetone) reacts with II ( a–c ), these ligands retain their identity and form cis-[M^VIO₂] complexes, [{Mo^VIO₂}{en(3,5-dtbb)₂(6,8-dtbbenzox)}] ( 4 ), [{Mo^VIO₂}{en(3-tb,5-mb)₂(6-tb,8-mbbenzox)}] ( 5 ) and [{Mo^VIO₂}{en(3,5-dmb)₂(6,8-dmbenzox)}] ( 6 ), [{W^VIO₂}{en(3,5-dtbb)₂(6,8-dtbbenzox)}] ( 7 ), and [{W^VIO₂}{en(3-tb,5-mb)₂(6-tb,8-mbbenzox)}] ( 8 ). However, the benzoxazine ring ruptures in case of ligand IIc under these conditions and form [{W^VIO₂}{en(3,5-dmb)₃}] ( 10 ), similar to complexes 1–3 . Complex [{W^VIO₂}{en(3,5-dmb)₂(6,8-dmbenzox)}] ( 9 ), having structure similar to 4–8 , could only be obtained when the reaction was carried out in toluene. Not only 9 , even complexes 4–8 can be isolated in toluene. Rupturing of both benzoxazine rings has also been experienced when ligands 1,2-bis(6,8-disubstitutedbenzo[e][1,3]oxazin-3(4H)-yl)ethane [ I ( a–c )] react with [M^VIO₂(acac)₂] (M=Mo or W) in MeOH and give salan type complexes [(M^VIO₂)en(3,5-dtbb)₂] [M=Mo ( 11 ), M=W ( 14 )], [(M^VIO₂)en(3-tb,5-mb)₄] [M=Mo ( 12 ), M=W ( 15 )] and [(M^VIO₂)en(3,5-dmb)₄] [M=Mo ( 13 ), M=W ( 16 )]. Complexes 1–9 have been used as catalyst for the multicomponent Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) and oxidative bromination of phenol derivatives.     

Syntheses and structures of molybdenum and tungsten pentabenzylcyclopentadienyl complexes: new chlorination reactions

[M(CpBz)(CO)₃CH₃] (M=Mo, 2a, W, 2b; CpBz=C₅(CH₂Ph)₅) have been prepared and reacted with PCl₅ and PhI · Cl₂. Depending on the metal and on the chlorinating reagent used [Mo(CpBz)(η²-COCH₃)Cl₃], 3, [W(CpBz)Cl₄], 4, [Mo(CpBz)(CO)₃Cl], 5 and [Mo(CpBz)Cl₄], 6 have been obtained. The molecular structures of all compounds are reported and two conformations have been characterised for the benzyl substituents. In complexes 2a, 2b and 5 one phenyl ring bends towards the metals while in 3 and 4 the five phenyls point opposite to the metals.     

Synthesis of Nitrido(phthalocyaninato)metal(V) Complexes RnPcMN (M = Re,Mo, W) and New Compounds with Nitrido‐Bridges between Rhenium and Elements of the Third Main Group

New tetra‐ and octasubstituted nitrido(phthalocyaninato)metal(V) complexes R_nPcMN (M = Re, Mo, W) were synthesized to obtain soluble nitrido‐bridged phthalocyanines. Phthalocyanines with nitrido bridges between rhenium and boron, aluminium, gallium and indium, respectively, were synthesized from nitrido(tetra‐tert.‐butylphthalocyaninato)rhenium(V) complex, tBu₄PcReN and suitable electrophilic reagents like BCl₃, B(C₆F₅)₃, BPh₃, BEt₃, AlCl₃, GaCl₃, GaBr₃, InCl₃, etc. The nitrido‐bridged compounds prepared show different stabilities depending on the substituents at the boron atom. Additionally, the possibility to increase the nucleophilicity of (C₅H₁₁)₈PcWN by reducing this complex with C₈K was studied. The reaction of the reduced complex with electrophiles, e.g. with tBuMeSiCl, Ph₃SiCl and Me₃GeCl indicates the formation of nitrogen‐bridged complexes.     

Structural analysis of several W(VI) and Mo(VI) complex perovskites prepared by the polymeric precursors method

We describe in this work the synthesis by the Pechini method of five Mo(VI)- and W(VI)-containing complex perovskites and their structural characterisation by HREM and XRD. The compounds studied, Ba(B_2/3′B_1/3″)O₃ (B′=In and Y; B″=W and Mo) and Sr(In_2/3W_1/3)O₃, were obtained after firing the precursor powders for 8 h at 1200°C. Thermal analysis showed that the formation mechanism of the five perovskites is similar and implies the formation of barium carbonate and barium tungstates or molybdates of different stoichiometries as intermediate phases. Interesting enough, these similar mechanisms yield to materials of a quite different structure. Indeed, Ba(In_2/3Mo_1/3)O₃ and Sr(In_2/3W_1/3)O₃ were found to be disordered perovskites (unit cells: a_p×a_p×a_p and , respectively); on the other hand, two phases coexist in the sample Ba(In_2/3W_1/3)O₃ at the synthesis conditions: an ordered predominant phase (unit cell: 2a_p×2a_p×2a_p) and, as a minor phase, a disordered perovskite (unit cell: a_p×a_p×a_p). Finally, the two yttrium-containing compounds were found to be ordered perovskites (2a_p×2a_p×2a_p).