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Crystal structure at -100.deg. of ammonium oxoperoxo(pyridine-2,6-dicarboxylato)vanadate(V) hydrate, NH4[VO(O2)(H2O)(C5H3N(COO)2)].xH2O (x .aeq. 1.3)
Abstract
The crystal structure at -100° of the compound NH4[VO(O2)(H2O)(C5H 3N(COO)2)]·xH2O (x ≈ 1.3) has been determined from three-dimensional X-ray intensity data collected by counter methods on a computer-controlled diffractometer using a Joule-Thomson low-temperature device. The compound crystallizes in the monoclinic space group C2/c with eight formula units in a cell having lattice constants a = 11.307 (2) Å, b = 25.490 (5) Å, c = 8.316 (2) Å, and β = 96.90 (1)° (at temperature -100 (2)°). The structure was solved by direct methods and refinement by full-matrix least-squares methods has given a conventional R value of 3.1% for the 1331 observed reflections. The structure is comprised of two crystallographically different ammonium ions (one lying on a twofold axis and the other on a center of symmetry) and a vanadium-based anion. These ions are held together by both electrostatic forces and extensive hydrogen bonding. The vanadium atom environment is a seven-coordinate distorted pentagonal bipyramid, with a vanadyl oxygen and a water molecule at the apices and a peroxy group, the nitrogen from the pyridine ring, and one oxygen atom from each carboxylate group forming an approximate pentagonal plane. The vanadium atom is displaced 0.25 Å from the "plane" toward the vanadyl oxygen atom. Interatomic distances within the anion are 1.870 (2) and 1.872 (2) Å for the V-Qperoxo bonds, 1.579 (2) A for the V=O bond, 2.053 (2) and 2.064 (2) Å for the V-Ocarboxylate distances, 2.211 (2) Å for the V-Owater distance, 2.088 (2) Å for the V-N distance, and 1.441 (2) Å for the O-Operoxo bond.
... During investigations to identify new water-soluble vanadium compounds that could be used as precursors for V-based oxides, the title compound was isolated. The structure of the analogous hydrate derivative, (NH 4)[VO(O2)(H2O)(C7H3NO4)] · xH2O (x~1.3) was reported by Drew et al. from Weissenberg films data [3]. In our analysis, we do not observed any water molecule in the unit cell and the structure of the [VO(O 2)(H2O)(C7H3NO4)] anion is similar to that reported in [3] but with a more precise geometry. ...
... The structure of the analogous hydrate derivative, (NH 4)[VO(O2)(H2O)(C7H3NO4)] · xH2O (x~1.3) was reported by Drew et al. from Weissenberg films data [3]. In our analysis, we do not observed any water molecule in the unit cell and the structure of the [VO(O 2)(H2O)(C7H3NO4)] anion is similar to that reported in [3] but with a more precise geometry. The vanadium coordination polyhedron is a pentagonal bipyramid with the peroxo and dipicolinato ligands being bidentate and tridentate, respectively. ...
... The coordination of vanadium by the pyridine-2,6-dicarboxylato ligand leads to the formation of two five-membered chelate rings. The [3]. Moreover, the O-O distance in the peroxo group is 1.437(4) Å, which does not differ significantly from the values found in the peroxide ion (1.49 ...
C7H9N2O8V, orthorhombic, Pcca (No. 54), a = 13.575(4) Å, b = 20.603(6) Å, c = 8.026(3) Å, V = 2244.8 ų, Z = 8, Rgt(F) = 0.046, wRref(F²) = 0.155, T = 293 K.
... Ammonium oxoperoxo(pyridine-2,6-dicarboxylato) vanadate(V) hydrate, NH 4 17 O labeled peroxo ligand was prepared as described previously [5,26]. The 17 O isotope enrichment of the peroxido ligand was 45%. ...
... Two crystal structures of HS003 have been reported in the literature which include crystallographic water molecule (CCDC number: 1236862) or a NH 4 + counterions (CCDC number: 233791). DFT calculations were performed using the Gaussian09 software package [29] using the crystal structure of HS003 with and without crystallographic water molecules and NH 4 + counterion [5]. NMR parameter calculation was performed by the GIAO method using B3LYP hybrid functional and 6-311G(d,p) and 6-311++G(d,p) basis sets. ...
... These simulations, performed considering a single 17 O site, are in good agreement with the experimental spectra suggesting that the two isotopically labeled oxygen atoms of the peroxido ligand have similar magnetic environments, as anticipated from the X-ray studies. [5] The simulations yield δ iso = 620 ppm, δ σ = 440 ppm, η σ = 0.15, C Q = 15.5 MHz and η Q = 0.55, α = 14, β = 10 and γ = 46, where α, β, γ represent the Euler angles denoting the relative orientation between the chemical shift and quadrupolar tensors. 17 O isotropic solution shifts of ca. ...
Electronic and structural properties of short-lived metal-peroxido complexes, which are key intermediates in many enzymatic reactions, are not fully understood. While detected in various enzymes, their catalytic properties remain elusive because of their transient nature, making them difficult to study spectroscopically. We integrated ¹⁷O solid-state NMR and density functional theory (DFT) to directly detect and characterize the peroxido ligand in a bioinorganic V(V) complex mimicking intermediates non-heme vanadium haloperoxidases. ¹⁷O chemical shift and quadrupolar tensors, measured by solid-state NMR spectroscopy, probe the electronic structure of the peroxido ligand and its interaction with the metal. DFT analysis reveals the unusually large chemical shift anisotropy arising from the metal orbitals contributing towards the magnetic shielding of the ligand. The results illustrate the power of an integrated approach for studies of oxygen centers in enzyme reaction intermediates.
... During investigations to identify new water-soluble vanadium compounds that could be used as precursors for V-based oxides, the title compound was isolated. The structure of the analogous hydrate derivative, (NH4)[V0(02)(H 2 0)(C 7 H3N04)] · ΛΉ2Ο (χ ~ 1.3) was reported by Drew et al. from Weissenberg films data [3]. In our analysis, we do not observed any water molecule in the unit cell and the structure of the [ν0(0 2 )(Η20χ07Η 3 Ν04)Γ anion is similar to that reported in [3] but with a more precise geometry. ...
... The structure of the analogous hydrate derivative, (NH4)[V0(02)(H 2 0)(C 7 H3N04)] · ΛΉ2Ο (χ ~ 1.3) was reported by Drew et al. from Weissenberg films data [3]. In our analysis, we do not observed any water molecule in the unit cell and the structure of the [ν0(0 2 )(Η20χ07Η 3 Ν04)Γ anion is similar to that reported in [3] but with a more precise geometry. The vanadium coordination polyhedron is a pentagonal bipyramid with the peroxo and dipicolinato ligands being bidentate and tridentate, respectively. ...
C7H9N2O8V, orthorhombic, Pcca (No. 54), a = 13.575(4) Å, b = 20.603(6) Å, c = 8.026(3) Å, V= 2244.8 Å3, Z= 8, Rgt(F) = 0.046, wR ref(F2) = 0.155, T = 293 K.
... The three complexes containing the pdc ligands constitute an interesting series differing only in the position which the 'free' carboxylate group occupies on the pyridine ring. If the two carboxylate groups occupy the 2-and 6-positions (i.e., 2,6-pdc) this results in the pseudo-octahedral monoperoxovanadium complex NH4[VO(O2)(2,6-pdc)(H20)] .H20 [25]. Both carboxylate ligands and the nitrogen atom are bonded to the vanadium together with the oxo group, a peroxo ligand and a water molecule. ...
A series of bisperoxovanadium complexes (bpV) of the general formula K3[VO(O2)2(L-L′)] has been prepared and characerized. where L-L′ is a pyridinedicarboxylate (2,3-pdc, 2,4-pdc, 2,5-pdc) or 3-acetatoxypicolinate (3-acetpic). Two structures have been determined: bpV(2,4-pdc), P21, , , , Z = 8, R/Rw = 0.049/0.055, and bpV(3-acetpic), P1, , , , α = 110.742(16)°, β = 95.600(19)°, γ = 100.195(19)°, , Z = 2, R/Rw=0.036/0.026. The oxygen atom of the 2-carboxylate group and the oxo ligand are situated in apical positions of a pseudotrigonal plane formed by the nitrogen atom and the centres of the two peroxo groups. The compounds rapidly oxidize sodium tris(3-sulfonatophenyl)phosphine, in water, to the corresponding oxide. The results are discussed with reference to the reported insulin mimetic activity of this class of compounds.
... For comparison, the structure of Cs[VO 2 (dipic)] AE H 2 O is also monomeric, but no contact between the ligand-based oxygen atoms and the cesium cation was reported [40]. NH 4 [VO(O 2 )(H 2 O)(dipic)] AE xH 2 O also possesses monomeric vanadium-based anions, but the ammonium cations are hydrogen-bonded to ligand-based oxygen atoms [41]. The dimeric complex [{CH 3 NHC(NH 2 ) 2 }-{VO 2 (dipic)}] 2 has also been structurally characterized, and, interestingly, the two bridging oxo ligands remain multiply-bonded to one of the vanadium centers and only interact datively with the second vanadium center [42]. ...
Reaction of NH4VO3 with 2,6-pyridinedimethanol in water at 85 °C followed by the room temperature addition of HCl (aq) yields [HVO2(pydim)]x (pydim=2,6-pyridinedimethanolato dianion), as a sparingly soluble off-white solid. This acid may be deprotonated by titration with NaOH (aq), yielding Na[VO2(pydim)]·4H2O, which has been structurally characterized by single-crystal X-ray diffraction. Treating Na[VO2(pydim)]·4H2O with HCl (aq) regenerates [HVO2(pydim)]x, but reaction with additional NaOH (aq) displaces the pyridinedimethanolato ligand from the vanadium center. Similarly, treating [HVO2(pydim)]x with excess HCl (aq) strips the pyridinedimethanolato ligand from the vanadium center and yields the adduct [H3(pydim)]+Cl− as one component in a mixture of products. This adduct has been structurally characterized by single-crystal X-ray diffraction. The optimum pH range for stable dioxovanadium(V) complexes stabilized by the 2,6-pyridinedimethanolato ligand is at least 1.5–9.4.
Peroxido complexes represent an important group of vanadium compounds having practical applications in distinct areas of chemistry. They possess insulin mimetic properties, antitumor activity and stimulate or inhibit certain enzymes. The bioinorganic chemistry of peroxidovanadates studies also the role of vanadium in the active centers of vanadium dependent enzymes (haloperoxidases and nitrogenases). Peroxidovanadium compounds are intensively studied for their oxidative properties. They can act as catalysts or stoichiometric oxidants in oxidation reactions of organic compounds, e.g. in epoxidation, sulfoxidation, hydroxylation or bromination. This versatility of vanadium peroxido complexes necessitates a critical review of their molecular structure and properties both in solution and in solid state. In this inclusive review we present the complete set of peroxido complexes of vanadium heretofore characterized by X-ray diffraction analysis. Along with the molecular structures we present and discuss the solid state vibrational spectra and thermal decomposition data. Vibrational, UV-vis and 51V NMR spectra of complexes dissolved in various solvents are also discussed. We have extracted the data from several speciation studies in order to clarify the formation conditions for different types of peroxidovanadates and summarize their 51V NMR chemical shifts. We also refer to certain applications of peroxido complexes of vanadium and we place the emphasis on potential applications which have not yet been thoroughly examined but deserve more attention.
The complex [Nb2S4(Py(COO)(2))(2)(H2O)(2)] . 3H(2)O was synthesized and studied by X-ray diffraction analysis. The crystals are monoclinic, space group P2(1)/n, a = 21.075(2), b = 11.203(1), c = 21.749(2) Angstrom, beta = 1 10.631(9)degrees, V = 4805.7(8) Angstrom(3), Z = 8. The structure contains two crystallographically independent types of molecules having identical structure and close geometric parameters. The complex synthesized is the first structurally characterized niobium complexonate.
The combustion of hydrocarbons and other organic materials is the best known oxidation process. The burning of fuels for various purposes is the basis of man’s industrial activities. Free radical reactions with dioxygen are responsible for the generation of large amounts of heat and the appearance of flame. Selectivity is nonexistent in these spontaneous, high temperature processes.
In recent years, the liquid phase oxidation of organic substrates using transition metal compounds as catalysts has become a profitable means of obtaining industrially important chemicals. Millions of tons of valuable petrochemicals are produced in this manner annually [1]. Typical examples of such processes are the production of vinyl acetate or acetaldehyde via the Wacker process, equations (1) and (2); the Mid-Century process for the oxidation of methyl aromatics, such as p-xylene to terephthalic acid, equation (3); and the production of propylene oxide from propylene using alkyl hydroperoxides, equation (4).
Some aspects of the structural chemistry of monomeric, dimeric, and polymeric pseudooctahedral oxomonoperoxovanadium(V) complexes, such as the geometry of a VO(O2) moiety, the correlation between V-O(O 2) and O-O bond lengths, the structural manifestations of the trans influence of the multiple-bonded peroxo ligand, and the trends in distortion of the coordination pseudooctahedron, have been surveyed. The reasons for the positional inversion of the asymmetric N,O-bidentate chelating picolinate ligand are considered.
In this chapter, the chemistry of selected vanadium compounds and their ability to inhibit phosphatases and exhibit insulin-mimetic activities will be described. First, chemical properties are presented for three target groups of vanadium compounds inducing insulin-mimetic responses. The simple vanadate salts represent the group of vanadium compounds most studied and exhibit the most complex chemistry. The chemistry of a new peroxovanadium(V) compound is presented and a corresponding, isoelectronic hydroxylamido vanadium(V) complex is characterized. The similarities and differences between peroxovanadium and hydroxylamido compounds are identified. Bis(2,4-pentanedionato-O,O′)oxovanadium(IV) (VO(acac)2) derivatives undergo hydrolysis reactions in aqueous solution which must be unraveled in order to appropriately interpret biological studies. Second, the effect of coordination number of vanadium compounds on their potency as a transition state analog inhibitor for a phosphatase is described. The five-coordinate vanadium(V) dipicolinic acid complex is found to be a more potent inhibitor than the six-coordinate vanadium(IV) dipicolinic acid complex and the seven-coordinate peroxooxovanadium(V) dipicolinic acid complex because of the structural analogy with the transition state of phosphate ester hydrolysis. Third, the effects of four types of peroxovanadium(V) compounds in phosphatase, insulin receptor and glucose-uptake assays are determined. The results show that although a series of peroxo compounds have significantly higher activity than vanadate in cell culture assays, such large differences are no longer apparent in the rat epitochlearis muscle.
We present 51V solid-state magic angle spinning NMR spectroscopy as a probe of geometric and electronic environments in vanadium haloperoxidases and in oxovanadium (V) complexes mimicking the active site of these enzymes. In the bioinorganic complexes, 51V MAS spectra are sensitive reporters of the coordination environment and coordination geometry. In vanadium chloro- and bromoperoxidases, the spectra reveal unique electronic environments of the vanadate cofactor in each species. The experimental NMR observables and DFT calculations of the NMR parameters yield the most likely protonation states of the individual oxygen ligands in vanadium chloroperoxidase. A combination of experimental solid-state NMR and quantum mechanical calculations thus offers a powerful strategy for analysis of diamagnetic spectroscopically silent vanadium (V) states in inorganic and biological systems.
This chapter focusses on the properties of the novel vanadium-containing bromoperoxidases. Vanadium has been shown to be an essential requirement in the biological systems and the chemistry of the element is gaining considerable interest. As the chemistry of vanadium is of direct relevance to the mechanism of action of bromoperoxidases, the chemistry of vanadate, properties of vanadium (V) complexes, and their reactivity, including reactions with peroxide, are discussed in the chapter. The work in three selected areas, vanadium in mushrooms, vanadium in oil and coal, and vanadium in tunicates, are also discussed in the chapter. Vanadium is also an essential element for some marine macro-algae, such as the brown seaweed F. spiralus and the green seaweed Enteromorpha compressa. Most assay methods to detect bromoperoxidase activity are based on the bromination of monochlorodimedone, a cyclic diketone that has high affinity for HOBr. The steady-state kinetics of the reaction of vanadium bromoperoxidase with hydrogen peroxide and bromide has been extensively studied. Hypobromous acid is known to be in rapid equilibrium with molecular bromine and tribromide ions in aqueous solutions. The first electron paramagnetic resonance (EPR) spectrum reported of an extract of the cap of the mushroom showed clearly an EPR signal characteristic of oxo-vanadium (IV). Tunicates, commonly called “sea squirts,” are very successful marine organisms found in all oceans of the world.
Vanadium is a trace element that plays an important, perhaps essential and general role in the regulation of enzymatic phosphorylations. Several forms of life, including the fly agaric toadstool (Amanita muscaria) and certain sea squirts (ascidians), are able to concentrate vanadium. In other organisms vanadium is part of the active site of some enzymes. Well-studied examples are the nitrogen-fixing bacterium Azotobacter and various seaweeds that use vanadate-dependent peroxidases to synthesize halogenated organic compounds. Despite its importance as a “biometal” both in primitive, prokaryotic organisms (Azotobacter) and in the highly organized ascidians, which represent an early stage in the evolution of vertebrates, the bioinorganic chemistry of vanadium is still in its infancy. Just as young, but undergoing explosive development, is the chemistry of model compounds for vanadium-containing biomolecules, a domain of the bioinorganic coordination chemist, who almost daily discovers compounds with new and surprising structural features. This article reviews this fascinating area of bioinorganic chemistry.
The review is dealing with monoperoxidovanadium (V) complexes, intensively studied in many laboratories during the last decades, due to their importance in biocoordination chemistry which is based mainly on the fact that they represent synthetic structural and functional models for the peroxo form of the vanadium haloperoxidase enzyme (VHPO), or can exhibit insulin mimetic properties or antitumor activity. We discuss here the methods of synthesis from the viewpoint of composition of reaction solutions and reaction conditions. A complete summarization of seventy two structurally characterized mono- and dinuclear monoperoxidovanadium (V) complexes, with their chemical composition, set of donor atoms and space groups, is given. The general features in their molecular structure and intermolecular interactions are discussed. Besides UV-vis, their IR, Raman and 51V NMR spectral data are presented.
The infrared spectra of some vanadium(V) peroxo complexes were measured and supplemented with published data ( a total of 33 complexes) to seek for relations between the stretching vibrations of the V(O 2 ) group and the structure of the complexes. While no such relation could be established in the region of 9.10 - 800 cm ⁻¹ , in the 660 - 490 cm ⁻¹ range the spectral patterns were found sensitive to the composition and structure of the coordination polyhedron, thus making it possible to discriminate between complexes of different types.
Die Komplexe K[VO(O2)2H2O], K3[VO(O2)2CO3], K3[VO(O2)2C2O4] und K3[VO(O2)(C2O4)2] · H2O wurden dargestellt. Zusammensetzung und IR-Spektren der Verbindungen lassen auf eine monomere, pentagonal-pyramidale oder pentagonal-bipyramidale Konfiguration der Anionen schließen.Oxo-peroxocomplexes of Vanadium(V)The complexes K[VO(O2)2H2O], K3[VO(O2)2CO3], K3[VO(O2)2C2O4], and K3[VO(O2)(C2O4)2] · H2O have been prepared. On the basis of the composition and the IR spectra it is supposed, that the anions are monomeric with the pentagonal pyramidal or pentagonal bipyramidal structure.
Three supramolecular complexes, [VO(phen)(C2O4)(H2O)]·CH3OH (1) [(VO)2(u2-C2O4)(C2O4)2(H2O)2]·L·H2O (2), and [(4,4′-bipyH2)0.5]+[VO2(2,6-dipic)]−·2H2O (3) (phen = 1,10-phenanthroline 4,4′-bipy = 4,4′-bipyridine, 2,6-dipic = 2,6-pyridinedicarboxylic, L = 1,4-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)benzene), have been prepared and characterized by elemental analysis, IR, and UV–vis spectroscopy and single-crystal diffraction analysis. Structural analysis shows that the three complexes all contain carboxylate and V=O moiety; vanadium of 1 and 2 are six coordinate with distorted octahedral geometry with N2O4 and O6 donor sets, respectively, while 3 is five coordinate with distorted trigonal bipyramidal geometry with a NO4 donor set. The complexes exhibit catalytic bromination activity in the single-pot reaction for the conversion of phenol red to bromophenol blue in H2O–DMF at 30 ± 0.5 C with pH 5.8, indicating that they can be considered as functional model vanadium-dependent haloperoxidases. In addition, electrochemical behaviors are also studied.
Crystals of the formula K2[VO(O2)NTA] with NTA = nitrilotriacetate have been prepared and characterized by IR and single-crystal X-ray diffraction methods. The structure of the anion of the complex shows that the vanadium atom has a distorted pentagonal bipyramidal environment surrounded by one oxo group, one peroxo group, three oxygen atoms and one nitrogen atom from the NTA ligand.
From the V2O5H2O2H2dipic–nica/pa/phen–H2O/H2OCH3CN reaction systems (H2dipic = dipicolinic acid, nica = nicotinamide, pa = picolinamide, phen = 1,10-phenanthroline), three monoperoxidovanadium(V) complexes have been synthesized and structurally characterized: (Hpa)[VO(O2)(dipic)(H2O)]⋅H2O (1), (Hnica)[VO(O2)(dipic)(H2O)] (2) and (Hphen)[VO(O2)(dipic)(H2O)]⋅H2O (3). The organic counterions in 1–3 are protonated on the aromatic nitrogen atoms, whereas the dipicolinato(2-) (=dipic) ligand adopts a tridentate chelating coordination mode in all three complexes. The NOO donor atoms of dipic occupy the three equatorial positions of the characteristic distorted pentagonal bipyramid around the central vanadium atom. The aqua ligand is located in the apical position trans to the short VO(oxido) bond. In addition to electrostatic cation–anion interactions, the supramolecular architecture of the title complexes is formed by: (i) a network of DH⋯O (D = N, O and C) hydrogen bonds, (ii) π–π interactions between offset pyridine rings of dipic (in 1 and 2) as well as between the rings of Hpa+, Hnica+ or Hphen+, (iii) anion–π interactions (in 1 and 3) between the oxygen atoms of the COO− group and rings of the dipic ligands, and (iv) the rarely recognized lone pair–π interaction between the carboxamide oxygen atoms of Hpa+ and pyridine rings in 1, as well as between the oxygen atoms from crystal water molecules and the pyridine rings of Hphen+ in 3. The anion–π and lone pair–π interactions were studied more in detail by DFT. A common feature for both these interactions was the lack of significant covalent contributions to the attraction between the respective partners. 51V NMR spectra of the acidic aqueous solutions of 1–3 showed that the structure of the complex anion is for 2 and 3 maintained even after dissolution (single shift δV = −597 ppm), whereas 1 partially decomposes with formation of monoperoxidovanadium(V) species: [VO(O2)(H2O)(pa)]+ (δV = −582 ppm) and [VO(O2)(H2O)y]+ (δV = −539 ppm).
A high-pressure stopped-flow vessel was made of acid-proof tantalum block which enabled us to follow reactions of vanadium(V) ion with hydrogen peroxide in strongly acidic media. The rate for the formation of the monoperoxo complex (VO(O2)+) is expressed as d [VO(O2)+]/dt = (k1[H+]−1 + k2 + k3 [H+])[VO2+]− [H2O2] where k1 (s−1) (25 °C)=60.2 [ΔH≠ (kJ mol−1 = 21.1 ± 2.6, ΔS≠ (J mol−1 K−1) = − 140 ± 9, ΔV≠ (cm3 mol−1) = 9.9 ± 1.7], k2 (mo1−1 dm3 s−1) (25 °C) = 3.47 × 103 [ΔH≠ = 46.5 ± 1.3, ΔS≠ = −21 ±4, ΔV≠ = 2.8 ± 1.0] and k3 (mol-2 dm6 s−1) (25 °C) = 1.63 × 103 [ΔH≠ = 20.1 ± 4.7, Δ [tl]S≠ = −116 ± 16, ΔV≠ = 14.2 ± 3.2]. The rates of formation and dissociation of the diperoxo complex are described as d [VO(O2)2−]/dt = kf [VO(O2)+] [H2O2] and − d [VO(O2)2−]/dt = kd [VO(O2)2−] [H+]2, respectively, where kf (mol−1 dm3 s−1) (25 °C) = 3.49 × 103 [ΔH≠ (kJ mol−1) = 40.2 ± 0.8, ΔS≠ (J mol−1 K−1) = −42±3, ΔV≠ (cm3 mol−1) =0.0±0.2]. and kd (mol−2 dm6 s−1) (25 °C) = 3.79 × 103 [ΔH≠ = 45.7 ± 1.7, ΔS≠ = −23 ∓ 6]. Positive volumes of activation for the monoperoxo complex formation have been attributed to an expanded transition state with the distorted pentagonal-bipyramidal structure.
The structures of the three title compounds have been determined by X-ray Crystallography. (I) is tetragonal, spacegroup [4/m with Z = 2, a = 13.345(7), c = 9.745(8) Å. (II) is triclinic, spacegroup P, Z = 2, a = 10.52(1), b = 11.70(1), c = 12.97(1) Å, α = 70.7(1), β = 113.8(1), γ = 108.8(1)°; (III) is orthorhombic, spacegroup Pnaa, Z = 8, a = 17.72(1), b = 18.14(1), c = 18.57(1) Å. Data for all three compounds have been collected on a diffractometer and 556 (I), 2316 (II), 1263 (III) above background reflections have been refined to R (0.099, 0.086, 0.082) respectively.(I) has disordered C4h symmetry following a well-known structure type. The features of the oxovanadium(IV) etioporphyrin structures in (II) and (III) are similar. Compound (III), the adduct with 1,4-dihydroxybenzene (quinol, H2Q) [VO(ETP)]2[H2Q], which crystallised from a solution of [VO(ETP)] in tetrahydrofuran stabilized with O.1% quinol, consists of [VO(ETP)] molecules linked by H-bonds through the VO groups to the quinol OH groups. We discuss the general phenomenon of H-bonding to VO groups and its possible relevance to binding of VO porphyrins to OH groups at catalyst surfaces.
The equilibrium formation of mono- and diperoxovanadium(V) compounds from vanadate esters and hydrogen peroxide in ethanol and dioxane—ethanol mixtures has been studied by electron spectroscopy. The acid—base behaviour of the peroxo species identified by the spectroscopic investigation was studied potentiometrically. The results show that in ethanol a monoperoxo species, which behaves as a weak acid, is formed at low hydrogen peroxide concentrations and that such a species is transformed into a diperoxo compound, which behaves as a strong acid, at higher [H2O2]0. In dioxane—ethanol, on the other hand, only the monoperoxo species can be detected, even at high hydrogen peroxide concentrations. The consistency of these findings with the outcome of previous kinetic investigations is discussed.
Formation of a vanadium(V) monoperoxo complex with coordinated N-(carbamoylmethyl)iminodiacetate2− (ada) was observed in the pH range 1.3–8.6. The MI[VO(O2)ada] · xH2O (MI= K+, Cs+; x = 4 for K+ and 1 for Cs+) and Ba[VO(O2) ada]2 · 3H2O complexes were isolated from aqueous solution. K[VO(O)2)ada]·H2O was obtained by thermal decomposition of the crystallohydrate. The crystal structure of K[VO(O2)ada] · 4H2O was determined by X-ray structure analysis. The vanadium atom is seven-coordinated by oxo, η2-peroxo and tetradentate ada2−-N,O1, O2, O3 ligands. The oxygen of the carbamoyl group is in the apical position trans to the VO group.
The crystal structures of the title compounds, [K][L]·3H2O(1) and [NH4][L]·H2O(2)(L = purpurate, [C8H4N5O6]–) have been determined at 295 K by X-ray diffraction and refined by full-matrix least squares to R 0.059 (517 ‘observed’ reflections) and 0.080 (874 ‘observed’ reflections) respectively. Crystals of both are orthorhombic. For (1)(space group Ibca), a= 21.75(1), b= 16.512(3), c= 7.4304(7)Å. Z= 8; for (2)(space group Pbnn), a= 4.5688(8), b= 15.309(5), c= 17.011 (4)Å, Z= 4. In both structures, the anion has crystallographic symmetry 2, the angles at the central nitrogen being 126.3(7)(1) and 125.8(4)°(2). The two approximately planar barbiturate rings of each anion are not coplanar with each other, the interaction between neighbouring carbonyl groups causing torsion about the central nitrogen–carbon bonds. In both structures anion–cation interaction and hydrogen bonding is extensive.
The crystal structure of [pyda·H][V(pydc)O2], (pyda·H = 2,6-diaminopyridinum), (pydc = 2,6-pyridinedicarboxylate) has been determined by the X-ray diffraction method. This ionic complex crystallizes in the monoclinic system, space group P21/m, with two molecules per unit cell. The unit-cell dimensions are a = 8.1489(11), b = 6.3515(8), c = 13.5190(18)Å, β = 91.962(3)°, and V = 699.30(16)Å3. The final R value is 0.0389 for 1185 measured reflections. The resulting V(V) complex forms a crystal in which the vanadium atom is at the center of a distorted trigonal bipyramidal arrangement consisting of three donor atoms of the a tridentate ligand of [pydc]2- and two oxygen atoms. There is also one [pyda·H]+ unit as a counter ion. This ionic complex is held together by both ion-pairing and hydrogen-bonding forces. 2004
Stretching vibration wavenumbers have been estimated for (NH4)2[VO(O2)2F] and (NH4)3[VO(O2)2F2] based on normal coordinate calculations employing a valence force field derived from bond length—force constant correlations. The results bear out the recently suggested re-assignment of the vanadium—ligand stretching vibrations. The effect of ligands on the asymmetry of the group is discussed using structural data for 19 vanadium (V) peroxo complexes. The asymmetry of the group is different in compounds with different coordination numbers. This difference is accompanied by characteristic shifts of the vanadium—peroxo oxygen stretching mode absorptions.
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Vanadium ist ein Ultraspurenelement, dem eine wichtige, möglicherweise essentielle und generelle Rolle bei der Regulation enzymatischer Phosphorylierungen zukommt. Einige Lebewesen vermögen Vanadium anzureichern. Hierzu gehören der Fliegenpilz und bestimmte Seescheiden (Ascidien). Andere Organismengruppen enthalten Enzyme mit Vanadium im aktiven Zentrum. Gut untersuchte Beispiele sind das Stickstoff-fixierende Bakterium Azotobacter und mehrere Tange, die mit Vanadat-abhängigen Peroxidasen halogenierte organische Verbindungen synthetisieren. Daß Vanadium sowohl in primitivsten, prokariontischen Individuen wie Azotobacter als auch in den schon hoch organisierten, auf der Vorstufe zu den eigentlichen Wirbeltieren stehenden Ascidien biologische Aufgaben übernimmt, unterstreicht seine bisher allerdings kaum erforschte Bedeutung als „Biometall”. In der Tat ist die Bioanorganische Chemie des Vanadiums ein noch junges Forschungsgebiet. Ebenso jung, gleichwohl in stürmischer Entwicklung, ist die Chemie der Modellverbindungen Vanadium-haltiger Biomoleküle, eine Domäne des bioanorganisch arbeitenden Koordinationschemikers, in dessen Hand fast täglich Verbindungen mit neuen und überraschenden Strukturelementen entstehen. Über den derzeitigen Stand wird im folgenden ein Abriß gegeben.
Einer der sehr seltenen Thiolatovanadium(II)‐Komplexe , [V(tmeda)(pyt) 2 ] 1 , entstand bei der Umsetzung von Natriumpyridin‐2‐thiolat [Na(pyt)] mit [VCl 2 (tmeda) 2 ]. Durch den kleinen Bißwinkel der pyt ⁻ ‐Liganden ist das Vanadiumzentrum in 1 verzerrt oktaedrisch umgeben. Eine ungewöhnliche μ 2 ‐η ² :η ² ‐Koordination dieses Liganden konnte in den zweikernigen Komplexen [Na(thf) 2 V(pyt) 4 ] und [V 2 O 2 (pyt) 4 ] 2 beobachtet werden, wobei die pyt ⁻ ‐Brücke in 2 unsymmetrisch ist. magnified image
The 17O NMR of bromoperoxidase in Tris buffer at pH 8 treated with 17O-enriched H2O2 reveals direct binding of peroxide to active site vanadium both in the symmetric and asymmetric modes, the latter possibly due to hydroperoxide. In addition, non-active site HVO2(O2)22− is detected. The results are counter-checked with NMR data on peroxovanadium model compounds.
Le compose du titre cristallise dans le systeme monoclinique, groupe P2 1 /c et sa structure est affinee jusqu'a R=0,035. Coordination bipyramidale pentagonale autour des atomes V. Les anions forment des chaines en zig-zag le long de l'axe c
Peroxovanadium(V) species of notional formula [VO(OO)] +, [HVO 2(OO) 2] 2-, [H 2VO 2(OO) 2] -, [VO(OO) 3] 3-, [HVO(OO) 3] 2-, [V(OO) 4] 3-, [H{VO(OO) 2} 2O] 3-, and [VO(NH 3)(OO) 2] - have been identified in aqueous solution by 51V n.m.r. spectroscopy; species [HVO 3(OO)] 2-, [VO 2(OO) 2] 3-, and [{V(OH 2)(OO) 2} 2O] are also indicated. The chemical shifts and pK a values indicate that peroxo-ligands bind to vanadium less covalently than oxo-ligands, provided that at least one oxo-ligand remains co-ordinated.
The potential biological activity of vanadium analogs of AMP, ADP, ATP, 2‘,3‘-cAMP, and 3‘,5‘-cAMP stimulated the full speciation study of the vanadate−adenosine(AdH) and vanadate−adenosine−imidazole(ImH) systems in aqueous solution, using a combination of potentiometry (glass electrode) and 51V NMR spectroscopy. The study of the H+−H2VO4-−AdH−ImH system was performed in 0.600 M Na(Cl) medium at 25 oC in the pH range 2−11. In the vanadate−adenosine system V2Ad22- and a new complex, V2Ad2-, with log β = 7.68 ± 0.01 and 11.89 ± 0.08, respectively (pKa = 4.21), explained all experimental observations. Although the V2Ad2--type complex has previously been reported in the vanadate−AMP system, the existence of such a complex in a vanadate−nucleoside system was not previously appreciated. In the vanadate−adenosine−imidazole system a ternary mixed ligand complex, VAdIm-, forms in addition to the V2Ad22- and V2Ad2- species. It exists between pH 5.5 and 11 and has a formation constant log β = 3.04 ± 0.02. This is the first ternary complex of this type that has been characterized in a qualitative (stoichiometry) and quantitative (formation constant) manner. Although the complex is fairly weak and requires a large excess of imidazole to form, it is significantly more stable than the 1:1 complexes that previously have been reported to form between vanadate and adenosine. Above all, it is much more stable than the complexes that eventually form between vanadate and imidazole. The possibilities that intramolecular imidazole stacking and/or intermolecular hydrogen bonding explain the enhanced stability in the ternary complex are discussed. Furthermore, the action of various vanadium−adenosine derivatives and the potential role of vanadate−adenosine−imidazole complexes in biological systems is evaluated.
A crystalline glycylglycine complex of monoperoxovanadate has been obtained and its X-ray structure determined. The coordination is pentagonal bipyramidal with the peroxo group and a tridentate glycylglycine occupying the equatorial positions. The axial positions of the anion are occupied by the oxo ligand and by one oxygen of the peroxo group of the adjacent anion. The latter interaction establishes the seventh bond and produces a dimeric structure in the crystalline material. NMR studies of its dissolution in water combined with previously reported results from equilibrium measurements show that the dimer dissociates in water to the monomeric precursor. It is proposed that this monomer corresponds to the complex responsible for the inhibition of the vanadium-catalyzed decomposition of hydrogen peroxide by glycylglycine. Crystal structure of [NEt4][VO(O2)(GlyGly)]·1.58H2O: monoclinic, space group P21; Z = 4; a = 10.618(2) Å; b = 14.803(2) Å; c = 11.809(2) Å; β= 101.37(2)°; V = 1819.7 Å3; T = 198 K; RF = 0.029 for 2664 data (Io ≥ 2.5σ(Io)) and 431 variables.
The temperature dependence of the NMR contact shifts of [Ni(en)3] (RCO2)2 (R = Cl3C, Cl2HC, ClH2C, and H) in water is interpreted in terms of the chelate ring conformational equilibria. As was found previously for acetate, benzoate, and nitrate, two separate equilibria are exhibited by these systems in the temperature range from 0 to 75°C. For the high-temperature process a more precise correlation is observed in these new results between the base strength of the anion and the parameters for ring inversion. The large values of ΔH and ΔS for the high-temperature equilibrium are interpreted as the result of the breaking of hydrogen bonds and the dissociation of ion pairs. These observations and recent x-ray crystal results suggest that association of cation and anion plays an important role in ethylenediamine ring conformational behavior.
The family of very unstable tetraperoxo compounds has been prepared from aqueous solutions containing H2O2 and salts of Mo(VI) or W(VI). The crystal structures of Na2[Mo(O2)4]·4H2O and Na2[W(O2)4]·4H2O have been determined from single-crystal data, while the crystal structures of Rb2[Mo(O2)4], Cs2[Mo(O2)4], Rb2[W(O2)4] and Cs2[W(O2)4] have been determined from powder X-ray diffraction data. The compounds were also characterised by IR spectroscopy and the number of peroxo groups was determined by titration methods. By means of the density functional theory (DFT) method, the geometry and stability of tetraperoxo complexes have been studied. Even though in all tetraperoxo complexes the central atom Mo(VI), W(VI) or V(V) is surrounded by four peroxo groups and the geometry of the [Me(O2)4]n− anion is essentially the same, the investigated compounds differ in stability and colour and crystallise in different crystallographic systems.
Two oxovanadium(V) salicylhydroximate complexes, [VO(SHA)(H2O)]·1.58H2O (1) and [V3O3(CSHA)3(H2O)3]·3CH3COCH3 (2) have been synthesized by reaction of VO43− with N-salicyl hydroxamic acid (SHAH3) and N-(5-chlorosalicyl) hydroxamic acid (CSHAH3), respectively, in methanol medium. Compound 1 on reaction with pyridine 2,6-dicarboxylic acid (PyDCH2) yields mononuclear complex [VO(SHAH2)(PyDC)] (3). Treatment of compound 3 with hydrogen peroxide at low pH (2-3) and low temperature (0–5°C) yields a stable oxoperoxovanadium(V) complex H[VO(O2)(PyDC)(H2O)]·2.5H2O (4). All four complexes (1–4) have been characterized by spectroscopic (IR, UV–Vis, 51V NMR) and single crystal X-ray analyses. Intermolecular hydrogen bonds link complex 1 into hexanuclear clusters consisting of six {VNO5} octahedra surrounded by twelve {VNO5} octahedra to form an annular ring. While the molecular packing in 2 generates a two-dimensional framework hydrogen bonds involving the solvent acetone molecules, the mononuclear complexes 3 and 4 exhibit three-dimensional supramolecular architecture. The compounds 1 and 2 behave as good catalysts for oxygenation of benzylic, aromatic, carbocyclic and aliphatic hydrocarbons to their corresponding hydroxylated and oxygenated products using H2O2 as terminal oxidant; the process affords very good yield and turnover number. The catalysis work shows that cyclohexane is a very easily oxidizable substrate giving the highest turnover number (TON) while n-hexane and n-heptane show limited yield, longer time involvement and lesser TON than other hydrocarbons.
The water-soluble complex [{VO(van-L-ser)H2O}2μ-O], where van-L-ser is the Schiff base formed from o-vanillin and L-serine, has been prepared and structurally characterised. Characteristics, including the hydrogen bonding network, are addressed in the context of biologically relevant vanadium compounds.
Summary The electronic spectra of KVO3-H2O2-L-HClO4(KOH) aqueous solutions, where L is ethylenediaminetetraacetate (edta), 1,2-cyclohexanediaminetetraacetate (cdta),N-(carbamoylethyl)-iminodiacetate (keida) or iminodiacetate (ida) ion were measured and, based on their pH dependence changes (ca. 0.5–7.0) and time, the formation of carboxylato-oxoperoxo complexes of vanadium(V) and their stabilities at room temperature were studied. The monoperoxo complexes with edta, keida and ida are formed immediately after mixing stock solutions, whereas the monoperoxo complex with cdta is formed only by slow decomposition of the stable diperoxo complex. The stabilities of the monoperoxo complexes decrease in following order: cdta>edta>keida>ida.
Kinetic investigations of the photolysis of the copolymers VA1, VA2 and VA3, characterized in Part 1, are described. These copolymers have side-chains carrying vanadium (V) chelate residues of structure −OV(Q2) = O(Q = 8-quinolyloxy) and also side-chains with hydroxyl groups. At λ = 365 nm the copolymers photoinitiate polymerization of methyl methacrylate and values of the rates of initiation and photodecomposition have been determined. When the Vv content is monitored at λ = 330 nm linear first-order plots are obtained, but at λ = 500 nm the initial reaction appears to be unusually fast. The final slopes in the two types of experiment are the same and permit evaluation of the first-order rate coefficient kd. The latter increases with the OH content of the polymer for a given light intensity. Rates of photodecomposition and initiation are equal. To elucidate the mechanisms of reaction, experiments were carried out with VOQ2OCH3 as a model. In methyl methacrylate and benzene solutions, addition of methanol increases kd. U.v.—visible spectroscopy indicates (thermal) complex formation between VOQ2OCH3 and CH3OH, which occurs apparently instantaneously in benzene, but relatively slowly in methyl methacrylate. It is proposed that photochemical complex formation between hydrogen bonded−OV(Q2) = O and −OH groups occurs in the polymer and is responsible for the apparent anomalies observed with a monitoring wavelength of 500 nm.
New optically active vanadium(IV) and (V) and mixed valence(IV,V) complexes containing a quadridentate ligand (S)-N-[1-(2-pyridyl)ethyl]iminodiacetate (S-peida2−) have been prepared: i.e. uninuclear distorted octahedral [VIVO(S-peida)(H2O)] and Li[Vv(O)2(S-peida)], a mixed valence binuclear Na[V2IV,VO3(S-peida)2], and an oxo-peroxo complex Na[VvO(O2(2−))(S-peida)]. The tertiary amino nitrogen of S-peida2− occupies the trans position to the oxo ligand in the first three complexes, but trans to the peroxo ligand in the last complex. Three absorption bands of [VIVO(S-peida)(H2O)] in the region from 10000 to 30000 cm−1 have been assigned to the d-d transitions, dxy→(dxz,dyz), dxy→dz2−y2, and dxy→dz2, in the order of increasing frequency. The mixed valence complex gives an intervalence transfer band and two d-d bands in the region from 9000 to 25000 cm−1. It gives a negative and a positive CD peak corresponding to the intervalence transition. The VV(O)2 and the VVO(O2) complex give a characteristic absorption shoulder at 25000 and a peak at 23500 cm−1 with corresponding weak negative CD peaks, respectively. They are assigned to charge transfer bands from oxo and peroxo to VV, respectively. The sign of CD peaks seems to be governed mostly by asymmetric arrangement of the ligating atoms and asymmetric deviation of ligating atoms from regular octahedron.
51V nuclear magnetic resonance spectroscopy has been utilized in the investigation of the reactions of vanadate with N,N-dimethylhydroxylamine in aqueous medium. The major components of the reaction products were mono- and bisliganded mononuclear vanadate compounds with 51V chemical shifts near −630 and −740 ppm, respectively. Variation of the concentration of the reactants enabled the determination of stoichiometry and formation constants of the products. The two major signals near −740 ppm were assigned to two stereoisomers of a bisligand product. The proton stoichiometrics and pKa values of the major products were determined from pH variation studies. A crystalline product of the type [V(O)(ONMe2)2]2O was isolated from the reaction of vanadate with dimethylhydroxylamine and its structure determined from X-ray diffraction studies. The compound possesses a dimeric oxo-bridge structure with a six-coordinate vanadium core. The arrangement about each vanadium may be described as approximately tetrahedral considering the center of the N—O bond in each dimethylhydroxamide ligand as one vertex. Hydrolysis of the crystalline solid in D2O provided two isomers that corresponded to the two bisligand products. A variable temperature 1H NMR study in D2O and 50% D2O/(CD3)2CO mixture revealed the existence of reasonably fast chemical exchange between the two predominant isomers. The nature of coordination of these and related compounds is discussed. Crystal structure of [V(O)(ONMe2)2]2O: orthorhombic, space group P22121;Z = 2;a = 7.0955(9) Å; b = 10.2313(12) Å; c = 11.5942(11) Å; V = 841.69 Å3; T = 213 K; RF = 0.021 for 1141 data (I0 ≥ 2.5σ(I0) ) and 137 variables. Keywords: bis(N,N-dimethylhydroxamido)hydroxooxovanadate, vanadate, dimethylhydroxylamine, vanadium NMR, aqueous equilibria, peroxovanadate.
The crystal structure of the compound NH4[VO(O2)2(NH3)] has been determined from three-dimensional X-ray data collected by counter methods. The compound crystallizes in the orthorhombic space group Pnma with four formula units in a cell of dimensions a = 8.370 (2) Å, b = 6.877 (1) Å, and o = 9.244 (2) Å. Refinement by full-matrix least-squares methods has given a conventional R value of 3.1% for the 566 observed reflections. The coordination of the vanadium atom can best be described in terms of a pentagonal pyramid, the four oxygens of the two peroxo groups and the ammonia nitrogen atom forming the distorted base of the pyramid, while the vanadyl oxygen occupies the apical position. Each ion has crystallographic mirror symmetry, the peroxy groups being the only nonhydrogen atoms lying off the mirror plane. Analysis of the motion of the anion as a rigid body yields interatomic distances of 1.883 (3) and 1.882 (3) Å for the V-O peroxo bonds, 1.606 (3) Å for the V=O bond, 2.110 (4) Å for the V-NH3 distance, and 1.472 (4) A for the O-O peroxo bond.
Triperoxovanadates of the type MI[V(O–O)3(AA)],nH2O and MI3[V(O–O)3(AA)′],H2O [M1= NH4, K or Na;(AA)= phen or bipy; (AA)′= C2O4(phen = 1,10-phenanthroline, bipy = 2,2′-bipyridyl)] have been prepared by reaction of the ligands with solutions of metavanadates in hydrogen peroxide. The molar conductivities of these salts in aqueous solution show the presence of 1 : 1 and 3 : 1 electrolytes. The existence, splitting, and shift of some i.r. bands including, in the 550–650 cm–1 region, bands assigned to the [graphic omitted] group show that the peroxophen, bipy and oxalato-groups are co-ordinated as bidentate ligands. U.v. spectra, magnetic susceptibilities, and an X-ray analysis are also reported. These complexes, in which the vanadium is probably eight-co-ordinate, are compared with the corresponding niobium and tantalum derivatives.
The stereochemistry of an atom in any particular molecule depends on the number of pairs of electrons in its valency shell. It is convenient to distinguish three types of electron pairs : (1) non-bonding or lone pairs, (2) σ-bonding pairs, (3) π-bonding pairs. The general arrangement of the valencies around any atom is determined by the fact that the lone pairs and the σ-bonding pairs of electrons arrange themselves as far apart as possible. To a first approximation the π-bonding pairs can be ignored. A more detailed and exact description of the shapes of molecules can be given if it is assumed (1) that a lone pair repels other electron pairs more than a bonding pair of electrons, (2) that a double bond repels other bonds more than a single bond; (3) that the repulsion between bonding pairs depends to some extent on the electronegativity of the ligand and decreases as the latter increases. The tendency of the electron pairs in a valency shell to keep apart is mainly due to the exclusion principle. Such relatively localised electron pairs are most conveniently described in terms of localised molecular orbitals or bond orbitals constructed from appropriate hybrid orbitals on the central atom and a suitable singly-occupied orbital on the ligand. When they are thus described by suitable localised orbitals the energy of interaction of the electron pairs is largely electrostatic, the non-classical or "exchange" part of the interaction energy being relatively small. When some of the electrons in a valency shell occupy d orbitals it is necessary to distinguish between the different d orbitals. It is often convenient to divide the d orbitals into two types, d γ and d ε orbitals; when one kind is used for bonding, non-bonding electrons of the same kind are equally as important as the bonding electron pairs in determining the shape of a molecule but electrons of the other kind have only a small effect on the stereochemistry. The ligand-field theory shows that the degeneracy of the five d orbitals is removed by the electric field of the ligands and that they split into two or more groups depending on the symmetry of the ligand field. It thus emphasises the necessity of distinguishing between the different types of d orbitals when discussing the stereochemistry of an atom which has valency-shell electrons in d orbitals. When the ligand-field theory is combined with the idea that valency-shell electrons described by suitably localised orbitals have a predominantly electrostatic interaction energy, then a detailed understanding of the shapes of transition-metal complex ions is possible.
Methyl vanadate VO(OCH3)3 crystallizes in the monoclinic space group P21/c with lattice constants a = 8.73, b = 15.28, and c = 9.55 A, β= 97°, Z = 8 molecules/unit cell. The vanadium is octahedrally coordinated, and the molecules form a linear polymer down the c axis of the crystal by the sharing of edges of the octahedra. Vanadium-oxygen distances can be grouped into five different groups: the short vanadyl oxygens with V-O distances of 1.51 and 1.57 A, single-bonded oxygens not involved in vanadium-vanadium bridging with V-O distances of 1.74 A, oxygens involved in weak vanadium-vanadium bridging with V-O distances of 1.84 and 1.86 A, oxygens involved in strong vanadium-vanadium bridging with V-O distances of 1.96 and 2.05 A, and the long vanadium-oxygen bonds of 2.2 and 2.3 A. Bonding of one polymer chain to adjacent ones is prevented by the presence of the methyl groups.
The x‐ray form factors for a bonded hydrogen in the hydrogen molecule have been calculated for a spherical approximation to the bonded atom. These factors may be better suited for the least‐squares refinement of x‐ray diffraction data from organic molecular crystals than those for the isolated hydrogen atom. It has been shown that within the spherical approximation for the bonded hydrogens in H2, a least‐squares refinement of the atomic positions will result in a bond length (Re value) short of neutron diffraction or spectroscopic values. The spherical atoms are optimally positioned 0.07 Å off each proton into the bond. A nonspherical density for the bonded hydrogen atom in the hydrogen molecule has also been defined and the corresponding complex scattering factors have been calculated. The electronic density for the hydrogen molecule in these calculations was based on a modified form of the Kolos—Roothaan wavefunction for H2. Scattering calculations were made tractable by expansion of a plane wave in spheroidal wavefunctions.
The crystal and molecular structure of tris(glycinato)chromium(III) monohydrate, Cr(C2H4NO2)3·H2O, has been determined by single-crystal X-ray analysis. The cell constants are a = 6.256 (1), b = 14.649 (1), c = 12.267 (1) Å, and β = 100.39(1)°. The space group is P21/c and with Z = 4 the calculated density is 1.755 g/cm3 compared to the observed 1.76(1) g/cm3. Scintillation counter diffractometry was used to measure the intensities of 2631 independent reflections significantly above background. The phase problem was solved by the application of direct methods and the structural parameters refined by a block-diagonal least-squares procedure to a final R of 0.0266. All hydrogen atoms in the structure were located and their positional parameters were refined. Anisotropic thermal parameters were used for all atoms except hydrogen. The chromium ion is octahedrally coordinated by three glycinato ligands so that the three nitrogen atoms are mutually cis. Average bond lengths are as follows (Å): Cr-N, 2.068 (5); Cr-O, 1.965 (2); N-C, 1.479 (3); C-C, 1.517 (2); C-O (coordinated), 1.290 (9); C-O(carbonyl), 1.223 (6). Individual molecules in the crystal are held together by a three-dimensional network of strong hydrogen bonds, including an unusual bifurcated linkage. The uv and visible spectra of the complex are presented and discussed.
Levy); ORTEP, Fortran thermal ellipsoid plot program for crystal structure illustrations
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Martin, and H. A. Levy); ORTEP, Fortran thermal ellipsoid
plot program for crystal structure illustrations (C. K.
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