Octahedral Vanadium Research Articles

A New Three-Dimensional Vanadium Selenite, (VO)2(SeO3)3, with Isolated and Edge-Shared VO6 Octahedra

Single crystals of (VO)2(SeO3)3 have been prepared from SeO2 and V2O5. The crystal structure has been determined by single-crystal X-ray diffraction. Crystal data: (VO)2(SeO3)3, Mr = 514.75; monoclinic, space group P21/a (No. 14); cell parameters a = 9.151(1) A, b = 6.353(1) A, c = 14.992(1)A, β = 93.538(5)°, and Z = 4. The structure consists of VO6 octahedra and SeO3 groups. The vanadium octahedra either are edge-sharing and form [V2O6.66]3.33- groups or are corner-linked through an [SeO3/2]+ cation. The structure may be rationalized in terms of connecting layers of {2[SeO2/2O1/3]4/3+[VO1/1O4/2O1/3]5/3-}+ cations and {[SeO3/2]+[VO1/1O5/2]2-}- anions.

Study of the Structure and Mechanism of Formation through Self-Assembly of Mesostructured Vanadium Oxide

The structure and mechanism of formation of a novel hexagonal mesostructured vanadium oxide−surfactant composite (HMVO), synthesized by acid-catalyzed hydrolysis of ethanolic cetyltrimethylammonium vanadate (CTAV) solution, has been studied by a variety of spectroscopic techniques. The poorly crystalline CTAV precursor used in the synthesis has been characterized and is shown to consist of pyrovanadate-like anions in which one oxygen atom is shared between vanadate tetrahedra. The HMVO formed from this precursor appears to feature a distorted octahedral vanadium coordination similar to that found in extended structures such as the two-dimensional vanadium pentoxide gel network. Information on the solution speciation during the synthesis is monitored by 51V NMR spectroscopy. Prior to acid addition, the ethanolic solution of CTAV shows a single narrow resonance at −556.7 ppm, assigned to a tetrahedral diester anion [VO2(OEt)2]-, undergoing fast reorientational averaging of the quadrupole interaction in solu...

A Divanadium(III) Complex Bridged by Cl− and OH− Anions

The crystal structure of the complex μ-chloro-μ-hydroxo-bis[dichlorobis(tetrahydrofuran-O)vanadium(III)] tetrahydrofuran solvate, [V2(μ-Cl)(μ-OH)Cl4(thf)4].thf (where thf is tetrahydrofuran, C4H8O), was determined. It was obtained from a tetrahydrofuran solution containing [VCl3(thf)3] and NaCPh3. The two octahedral vanadium(III) centers are bridged by a Cl− and an OH− anion, with a V⋯V separation of 3.281 (1) A. One vanadium(III) center has two axial Cl and two equatorial tetrahydrofuran ligands, while the other vanadium(III) center has two axial tetrahydrofuran and two equatorial Cl ligands. A tetrahydrofuran molecule which is contained as crystalline solvent is involved in hydrogen bonding with the bridging OH− anion.

Synthesis, Crystal Structure, and Magnetic Property of a Dinuclear Oxovanadium(IV) Complex with 2,6-Bis(salicylideneaminomethyl)-4-methylphenol

Abstract A dinuclear oxovanadium(IV) complex with 2,6-bis(salicylideneaminomethyl)-4-methylphenol (H3L), [(VO)2(L)(CH3O)(dmso)] (1) (dmso = dimethyl sulfoxide), has been synthesized and characterized by infrared and electronic spectra, and by the temperature dependence of magnetic susceptibilities (80—300 K). The molecular structure of 1 was determined by single-crystal X-ray structure analysis. The two octahedral vanadium ions are bridged by a phenoxo-oxygen of L, a methoxo ion, and a dimethyl sulfoxide and have syn oxo configuration. The magnetic property was discussed in relation to the crystal structure.

Syntheses and Properties of New Layered Alkali-Metal/Ammonium Vanadium(V) Methylphosphonates: M(VO(2))(3)(PO(3)CH(3))(2) (M = NH(4), K, Rb, Tl). Single-Crystal Structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2).

The hydrothermal syntheses of a family of new alkali-metal/ammonium vanadium(V) methylphosphonates, M(VO(2))(3)(PO(3)CH(3))(2) (M = K, NH(4), Rb, Tl), are described. The crystal structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) have been determined from single-crystal X-ray data. Crystal data: K(VO(2))(3)(PO(3)CH(3))(2), M(r) = 475.93, trigonal, R32 (No. 155), a = 7.139(3) Å, c = 19.109(5) Å, Z = 3; NH(4)(VO(2))(3)(PO(3)CH(3))(2), M(r) = 454.87, trigonal, R32 (No. 155), a = 7.150(3) Å, c = 19.459(5) Å, Z = 3. These isostructural, noncentrosymmetric phases are built up from hexagonal tungsten oxide (HTO) like sheets of vertex-sharing VO(6) octahedra, capped on both sides of the V/O sheets by PCH(3) entities (as [PO(3)CH(3)](2-) methylphosphonate groups). In both phases, the vanadium octahedra display a distinctive two short + two intermediate + two long V-O bond distance distribution within the VO(6) unit. Interlayer potassium or ammonium cations provide charge balance for the anionic (VO(2))(3)(PO(3)CH(3))(2) sheets. Powder X-ray, TGA, IR, and Raman data for these phases are reported and discussed. The structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) are compared and contrasted with related layered phases based on the HTO motif.

Hydrothermal Synthesis, Crystal Structure, and Magnetic Properties of Cs[(V2O3)(HPO4)2(H2O)], a Mixed-Valence Vanadium (IV, V) Hydrogen Phosphate with a One-Dimensional (-VIV-O-VV-O-) Chain of Corner-Sharing VO6 Octahedra

The hydrothermal reaction of Cs4V2O7, V, H3PO4, H2O, and Bu4NBr in the molar ratio 4.5:1:41:3150:1 at 200°C for 48 hr yielded the red-brown cesium vanadium phosphate Cs[(V2O3) (HPO4)2(H2O)], a mixed-valence V(IV, V) species. The structure contains corner-sharing vanadium octahedra and phosphorus tetrahedra with unusual 1-D (-VIV-O-VV-O-)∞ chains formed from VO6 octahedra sharing opposite corners. These chains are connected through tridentate bridging (HPO4)2- units to produce a three-dimensional network. The Cs+ cations occupy large channels formed from six vanadium octahedra and six phosphorus tetrahedra. At room temperature the material is paramagnetic with one unpaired spin per (-VIV-O-VV-O-) unit while complicated antiferromagnetic ordering is observed below ca. 6 K. Crystal data: monoclinic, P 21/n with a = 7.22(1), b = 18.56(1), c = 8.195(6) Å, β = 114.01(6)°, Z = 4, dcalc = 3.233 g cm-3; structure solution and refinement based on 1088 reflections converged at R = 0.028.

(H2NC4H8NH2)[(VO)2(PO4)2] and (H2NC4H8NH2)2[(VO)3(HPO4)2(PO4)2].cntdot.H2O: Novel Layered Vanadium Phosphates with Distorted and Defected VOPO4 Layers

Two new layered vanadium phosphates, (H[sub 2]NC[sub 4]H[sub 8]NH[sub 2])[(VO)[sub 2](PO[sub 4])[sub 2]] (1) and (H[sub 2]NC[sub 4]H[sub 8]NH[sub 2])[sub 2][(VO)[sub 3](HPO[sub 4])[sub 2](PO[sub 4])[sub 2]][center dot]H[sub 2]O (2), have been hydrothermally synthesized under similiar conditions. Compound 1 is synthesized from VCl[sub 4], H[sub 3]PO[sub 4], piperazine, (n-C[sub 4]H[sub 9])[sub 4]NOH, and H[sub 2]O in the mole ratio 1:2.7:2.1:1.2:350 at 200 [degrees]C for 70 h and autogeneous pressure. In contrast, the preparation of 2 required the presence of (CH[sub 3])PO[sub 3]H[sub 2], such that reaction of VCl[sub 4], H[sub 3]PO[sub 4], (CH[sub 3])PO[sub 3]H[sub 2], piperazine (n-C[sub 4]H[sub 9])[sub 4]NOH, and H[sub 2]O in the mole ratio 1:3.5:1.2:3.3:1.2:390 at 200 [degrees]C for 70 h yields 2 in 50% yield, with 1 as the other component. Green plates of compound 1 crystallize in the monoclinic space group P2[sub 1]/c with a = 8.786(2) [angstrom], b = 8.257(2) [angstrom], c = 8.566(2) [angstrom], [beta] = 111.07(3)[degrees], V = 579.9(3) [angstrom][sup [minus]3], Z = 2, and R = 0.0298 whereas blue plates of 2 crystallize in the noncentrosymmetric orthorhombic space group Pna2[sub 1] with a = 14.631(3) [angstrom], b = 8.706(2) [angstrom], c = 17.635(4) [angstrom], V = 2246.3(11) [angstrom][sup [minus]3], Z =more » 4, and R = 0.0363. Compound 1 has puckered layers containing triangular bipyramidal vanadium(IV) centers. Phosphate 2 has VOPO[sub 4[minus]] like layers with 1/4 of the V(IV) octahedral sites missing which results in unusual edge-sharing involving half the phosphate tetrahedral with the vanadium octahedra and protonation of the remaining phosphate groups to give HPO[sub 4[sup 2[minus]]] residues.« less

Macrocyclic oxovanadium(IV) complexes: structure, magnetochemistry and electrochemistry

The oxovanadium(IV) complexes, [VO(L)]·H2O 1, [VO(H2L)(SO4)]·3H2O 2, [(VO)2L(µ-SO4)]·MeOH·3H2O 3 and [Zn(L)VO(SO4)]·4H2O 4 have been synthesised from the dinucleating tetraaminodiphenol macrocyclic ligand H2L. The ESR and IR spectra of 1 have indicated stacking of the molecules due to ⋯ VO ⋯ VO ⋯ interactions. In complexes 2 and 4 the unidentate sulfate is bound to the octahedral vanadium and two of the secondary amino groups in 2 are protonated. Both of these complexes undergo oxidation to produce oxovanadium(V) species with E½= 0.40 V (2), 0.455 V (4)vs. saturated calomel electrode (SCE). Fairly strong antiferromagnetic exchange interaction has been found in 3 from variable-temperature susceptibility measurements, J=–128 cm–1. The crystal structure of 3 has been determined; tetragonal, space group P4122, a=b= 12.252(2), c= 40.819(5)A and Z= 8; refinement led to R= 0.053 and R′= 0.055 using 1825 unique reflections with I > 3σ(I). The two octahedral vanadium centres in the complex, separated by 3.077 A, are bridged by sulfate and have syn oxo configuration.

Linear trimeric and monomeric octahedral vanadium(II) diphenylacetate complexes

Linear trimeric and monomeric octahedral vanadium(II) diphenylacetate complexes

Spectrophotometric and ESR evidence for vanadium(IV) deferoxamine complexes

Complexes of vanadium(IV), vanadyl, are reported to be formed with the trihydroxamic acid deferoxamine (H 3DF +). One complex exhibits a reddish-violet color, with a major absorbance peak at 386 nm and a smaller peak at 520 nm. This complex is potentially useful for the microdetermination of vanadyl. The apparent molar absorptivity is 3.91 mM −1 cm −1, and the complex obeys Beer's law in the concentration range of 0.6–63 ppm. Electron spin resonance studies indicate the formation of two vanadyl complexes that are 1:1 in vanadyl and deferoxamine, but have two or three bound hydroxamate groups. ESR and spectrophotometric evidence indicate that the red, low pH form, involves an octahedral vanadium (4+) ion coordinated by three hydroxamate ligands. One of these hydroxamates is displaced by an oxygen at pH 2.8 according to the following equilibria: VO 2 + H 3DF + ⇔ V IV(DF) 2+ + H 3O +, V IV(DF) 2+ + H 2O ⇔ VO(HDF) ++ H +, where pk 2 = 2.8.

On the possibility of a small amount of V 2+ in spinels near FeV 2O 4

Samples of overall composition FeV 2O 4 have been prepared at 1100°C, with Po 2 varying between 10 −14.25 and 10 −8.30 bar, and studied by quantitative X-ray diffraction, Mössbauer effect, magnetization measurements, absorption and emission spectroscopies. It is confirmed that FeV 2O 4 does not exist in these conditions and corresponds to a mixture of V 2O 3 and a spinel phase. From experimental and thermodynamic arguments, it is proposed that a small amount of octahedral vanadium is divalent, whereas the octahedral iron is mixed-valent with an oxidation number near to 3. It appears that nominal FeV 2O 4 is unstable against oxidation of partially filled V 3+ 2+ band and that the Fermi energy of the stable spinel phase intersects three overlapping redox couples : the Fe 3+ 2+ couple on both tetrahedral and octahedral sites and the V 3+ 2+ couple on octahedral sites.

Composition of the active component of supported vanadium-magnesium catalysts according to 51 NMR data

Vanadium-magnesium supported catalysts and model compounds (magnesium vanadates) have been studied with use of 51V NMR. It has been established that on the catalyst surface there exist isolated tetrahedral and octahedral vanadium species, their associated forms and magnesium orthovanadate. Their relative concentrations were determined by both the surface concentration of vanadium and the nature of modifying agents (such as SO 4 2−). The influence of CO 2 and H 2O adsorption and catalyst reduction with butene-1 on the vanadium coordination state has been studied.

Investigation of silica-supported vanadium oxide catalysts: preparation and characterization by vanadium-51 NMR and x-ray photoelectron spectroscopy

Characterization by /sup 51/V NMR of the vanadium species adsorbed on silica-supported catalysts, prepared by impregnation of silica by solutions of ammonium vanadate at various pH values, has been followed from the initial step (impregnating solutions and wet samples) to the final step of preparation (calcined solids in dry air). At first, by use of the classical high-resolution NMR, the major species both in the impregnating solutions and on the wet solids have been identified for the different initial pH, and relative quantitative evaluations have been performed. Preparations at pH 11 give a major proportion of tetrahedra V/sub 4/O/sub 12//sup 4 -/ species, while at pH 4 vanadium oxide precipitates on silica. Second, the observations by solid-state NMR of these dried samples have shown that an important content of tetrahedral species was deposited on the solids prepared with the pH 11 initial solution (with a vanadium loading corresponding to the monolayer coverage limit, as determined further by XPS for the calcined series of samples), while only octahedral vanadium entities are detected for lower pH values. These species exhibit only few distortions; thus no support effect was evidenced in these dried samples. However, after further dehydration of the samples by calcinationmore » in dry air, the tetrahedral species (pH 11 samples) are much more affected than the octahedral entities, due probably to the formation of V-O-Si bonds, and this observation could be in correlation with the existence of the monolayer coverage limit observed only with these samples. The rehydration treatment breaks these bonds and restores a NMR signal of tetrahedral species.« less

Activity measurements and spectroscopic studies of the catalytic oxidation of toluene over V2O5/Al2O3-C catalysts

Vanadium oxide catalysts based on Al2O3-C (γ-Al2O3) as support contain at least four different forms of vanadium. The distribution between these depends on the vanadium loading. The activity (per gram of vanadium) of these catalysts for toluene oxidation increases with increasing loading. The selectivity for benzene formation decreases from 2% for the support to 0% for 0.5 wt% V, while the selectivity for benzaldehyde formation first appears at this concentration and rises to 29% for 10 wt% V. It is suggested that benzene is formed at Lewis acid sites on the support, whereas benzaldehyde is formed on vanadium sites. At low loadings (0.1 and 0.2 wt% V) single vandium species with tetrahedral coordination are formed. The oxidised forms have u.v. bands at 35 500 and 42000 cm–1 and the reduced forms have i.r. bands of adsorbed CO at 2200 cm–1(room temperature) and at 2190 and 2158 cm–1(133 K). At medium loadings, vanadium surface clusters with varying degrees of agglomeration are formed in addition to the other species. These are suggested to be single chain species with vanadium in tetrahedral coordination, double chain species with vanadium in square pyramidal coordination and aggregates of octahedral vanadium formed by the coupling of double chains. The oxidised forms have u.v. bands at 34 500 and 43000 cm–1 and the reduced forms have i.r. bands of adsorbed CO at 2178 cm–1(room temperature) and at 2178 and 2158 cm–1(133 K). The agglomerates are more active than the isolated species and show some selectivity for benzaldehyde. Both the activity and the selectivity appear to increase with the degree of agglomeration. At high vanadium loadings (10 wt% V), surface crystallites of vanadium oxide are formed in addition to the other species. The oxidised forms have u.v. bands at 30 000 and 43 000 cm–1 and the reduced forms have i.r. bands of adsorbed CO at 2181 cm–1(room temperature) and at 2181 and 2145 cm–1(133 K). These crystallites are more active and selective than other species with less agglomeration. It is suggested that the increased activity for the larger species is due to the possibility of a transition from corner to edge sharing octahedra at the release of oxygen, which increases the activity of the double-bonded oxygen.

Hexa-amminevanadium(II) bromide

Hexa-amminevanadium(II) bromide has been prepared from [V(OH 2) 6]Br 2 in ethanol or liquid ammonia; it is isomorphous with [Ni(NH 3) 6]Br 2 and has the diffuse reflectance spectrum of a regular octahedral vanadium(II) complex.

ChemInform Abstract: COMPLEXES OF VANADIUM(II) WITH HETEROCYCLIC AND ALIPHATIC AMINES

AbstractDie V(II)‐Komplexe (I)‐(V) werden im allgemeinen durch Umsetzung von V(II)‐halogeniden mit den Aminen in äthanolischer Lösung unter Stickstoff gebildet und ihre Strukturen anhand magnetischer sowie elektronen‐ und IR‐spektroskopischer Daten diskutiert.

Complexes of vanadium(II) with heterocyclic and aliphatic amines

Complexes of vanadium(11) with a range of heterocyclic and aliphatic amines have been isolated, generally from ethanolic solution under nitrogen. With pyridine (py) and β- and γ-picolines (β pic and γ pic) complexes of the general formula V(amine)4X2, in which X = Cl, Br, or I, have been obtained. Their reflectance spectra are dominated by charge transfer bands, but some d-d transitions have been assigned. These complexes are magnetically dilute with magnetic moments near to 3.87 B.M. The only bis(amine) complexes isolated with these ligands are V(β pic),Br, and V(γ pic)2Br2, and these show considerable antiferromagnetic interaction because of polymeric structures. The thermal behaviour of the complexes V(amine)4X2 resembles that of the corresponding nickel(11) complexes. No definite assignments of V-X stretching frequencies have been possible. With ethylenediamine (en), propane-1,2-diamine (α pda), propane-1,3-diamine (β pda) and diethylenetriamine (dien) the following magnetically dilute complexes have been isolated : [V(en)3] X2, [V(αpda)3] X2, [V(βpda)3] X2 and [V(dien)2] X2. These complexes with aliphatic chelates have electronic spectra typical of octahedral vanadium(11). The 8-aminoquinoline (amq) complexes, V(amq)2Cl2,- 2H20, V(amq)2Br2,2H2O and V(amq)3I2,2H20, have more complicated electronic spectra and are magnetically dilute as are some 1,l0-phenanthroline and 2,2'-bipyridyl complexes of general type [V(chelate)3] X2,nH2O.

The investigation of the apparent thermochromism of some vanadium(III) complexes

Several crystalline octahedral vanadium(III) complexes of the general type (C 2H 5) 4NVBr 4− x Cl x ·2CH 3CN where x = 0–4 were prepared and investigated. The color of the complexes changes gradually from yellow for the (C 2H 5) 4NVCl·2CH 3CN complex to red-brown for the (C 2H 5) 4NVBr 4·2CH 3CN complex. All the complexes have the unusual property of being yellow at 77°K. An investigation was made of the magnetic properties, visible and u.v. spectra, i.r. spectra, and nuclear quadrupole resonance spectra of some of the complexes in an attempt to explain the color change.

Covalent compounds of quadrivalent transition metals. Part I. Spectra and magnetic properties of vanadium(IV) alkoxides, dialkylamides, and NN-dimethyldithiocarbamate

From the electronic absorption spectra, variable-temperature magnetic susceptibility studies, and room-temperature e.s.r. spectra it is concluded that the monomeric d1 compounds V(OBut)4, V(NMe2)4, and V(NEt2)4 have considerably distorted tetrahedral configurations. The data on V(S2CNMe2)4 are consistent with 8-co-ordinated (possibly dodecahedral) vanadium(IV). Vanadium tetraethoxide is dimeric and a structure is suggested with 5-co-ordinated (trigonal bipyramidal) vanadium(IV). Vanadium tetramethoxide, which is trimeric, has magnetic properties consistent with a structure involving highly distorted octahedral vanadium(IV).

The magnetism and spectra of some octahedral vanadium(III) complexes

The magnetic susceptibilities in the temperature range 80–300°K and ultraviolet and visible spectra of sixteen hexaco-ordinated complexes of vanadium(III) have been measured. Spectral data are consistent with octahedral formulations. The magnetic data are compared with the theory for a 3T1g ground term perturbed by spin–orbit coupling, ligand field components of axial symmetry, and an orbital reduction factor. Values of the parameter A for a wide range of ligands are shown to be rather similar. The splitting of the ground term due to asymmetry of the ligand field varies from 150–300 cm.–1 for MX6 complexes to 500–1000 cm.–1 for complexes with dissimilar ligands or three bidentate ligands.