Reactions of vanadate with N,N- dimethylhydroxylamine: aqueous equilibria and the crystal structure of the uncharged oxygenbridged dimer of bis(N,N-dimethylhydroxamido)hydroxooxovanadate

1997 ◽  
Vol 75 (4) ◽  
pp. 429-440 ◽  
Author(s):  
Pradip C. Paul ◽  
Sarah J. Angus-Dunne ◽  
Raymond J. Batchelor ◽  
Frederick W.B. Einstein ◽  
Alan S. Tracey
Keyword(s):  
Crystal Structure ◽  
Chemical Exchange ◽  
Chemical Shifts ◽  
Variable Temperature ◽  
Crystalline Solid ◽  
Resonance Spectroscopy ◽  
Reaction Products ◽  
Orthorhombic Space Group ◽  
Ph Variation ◽  
Nmr Study

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.

Synthesis, X-ray crystal structure, and solid-state 13C NMR study of tris(9-crown-3)triphenylene

2001 ◽  
Vol 79 (2) ◽  
pp. 195-200 ◽  
Author(s):  
Gerald W Buchanan ◽  
Majid F Rastegar ◽  
Glenn PA Yap
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Crown Ether ◽  
Chemical Shifts ◽  
Aromatic Rings ◽  
X Ray ◽  
Nmr Study ◽  
Group A ◽  
C Nmr ◽  
Solid State 13C Nmr

Benzo-9-crown-3 ether trimerizes in the presence of FeCl3 and aqueous H2SO4 to produce tris(9-crown-3)triphenylene in 25.4% yield. This compound crystallizes in the monoclinic P21/c space group: a = 13.759(2) Å, b = 13.318(2) Å, c = 13.399(2) Å, β = 96.883(2)°, with Z = 4. The three 9-crown-3 ether units of the trimer possess different geometries and there is substantial deviation from coplanarity in the three aromatic rings. 13C NMR chemical shifts in the solid state are consistent with this lack of symmetry and are discussed in terms of the X-ray crystal-structure data.Key words: crown ether, trimerization, stereochemistry.

109Ag NMR-Study of the Selective Solvation of the Ag+ Ion in Solvent Mixtures of Water and the Organic Solvents: Pyridine, Acetonitrile, and Dimethyl Sulfoxide

1984 ◽  
Vol 39 (1) ◽  
pp. 83-94 ◽  
Author(s):  
L. Guinand. K. L. Hobt. E. Mittermaier ◽  
E. Rößler ◽  
A. Schwenk ◽  
H. Schneider
Keyword(s):  
Chemical Shift ◽  
Dimethyl Sulfoxide ◽  
Organic Solvents ◽  
Mole Fraction ◽  
Chemical Exchange ◽  
Chemical Shifts ◽  
Equilibrium Constants ◽  
Solvent Mixtures ◽  
Nmr Study ◽  
Solvent Molecules

In mixtures of water (W) and one of the organic solvents pyridine, acetonitrile, and dimethyl sulfoxide (O), the silver ion forms the following solvate complexes: AgW2, AgWO, and Ag02. The chemical shift of 109Ag is strongly affected by the ligating solvent molecules, and replacing the ligand W by one of the three organic ligands yields a higher Larmor frequency. In solvent mixtures, only a single resonance line has been observed because of rapid chemical exchange. The measured chemical shifts in the range up to 400 ppm are mean values of the chemical shifts of the different solvate species in a given mixture, weighted with their relative concentrations. The 109Ag chemical shifts were determined for 0.05 to 0.15 molal solutions of AgNO3, as functions of the mole fractions of the solvent components. Using a Gaussian least squares fitting routine, the individual chemical shifts of the Ag+ solvate complexes and the corresponding equilibrium constants were determined. This fit was successful for the whole mole fraction range of DMSO, while in the solvent systems with acetonitrile and with pyridine at higher concentrations of the organic component the chemical shift is influenced by more than two solvent molecules. In these cases equilibrium constants were calculated from chemical shift data for solutions of low mole fraction of acetonitrile and pyridine.

scholarly journals A variable-temperature study of a phase transition in barbituric acid dihydrate

2005 ◽  
Vol 61 (4) ◽  
pp. 464-472 ◽  
Author(s):  
Gary S. Nichol ◽  
William Clegg
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Barbituric Acid ◽  
Crystal Packing ◽  
Variable Temperature ◽  
Mirror Plane ◽  
Monoclinic Space Group ◽  
Orthorhombic Space Group ◽  
Acta Cryst ◽  
Space Group

The crystal structure of barbituric acid dihydrate (C4H4N2O3·2H2O) has twice been reported as orthorhombic, space group Pnma, with all atoms (except for CH2 H atoms) lying on the mirror plane [Al-Karaghouli et al. (1977). Acta Cryst. B33, 1655–1660; Jeffrey et al. (1961). Acta Cryst. 14, 881–887]. The present study has found that at low temperatures, below 200 K, the crystal structure is no longer orthorhombic but is non-merohedrally twinned monoclinic, space group P21/n. This phase is stable down to 100 K. Above 220 K the crystal structure is orthorhombic, and between 200 and 220 K the structure undergoes a phase change, with the monoclinic-to-orthorhombic phase transition itself taking place at around 216–217 K. The size of the β angle in the monoclinic structure is temperature dependent; at 100 K β is around 94° and it decreases in magnitude towards 90° as the temperature increases. Although the hydrogen-bonding motifs are the same for both crystal systems, there are significant differences in the crystal packing, in particular the out-of-plane displacement of the two water molecules and the sp 3-hybridized C atom of barbituric acid.

Crystal and molecular structure of Z- and E-1,2-dichloro-1,2-bis(2-chlorophenyl)ethylene. An X-ray and NMR study

1995 ◽  
Vol 73 (9) ◽  
pp. 1520-1525
Author(s):  
Luciano Antolini ◽  
Ugo Folli ◽  
Dario Iarossi ◽  
Adele Mucci ◽  
Silvia Sbardellati ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Nmr Study ◽  
Phenyl Rings ◽  
A Cell ◽  
C Nmr

The crystal structures of the title compounds were determined by single crystal X-ray diffraction techniques. The molecule of the Z isomer, which crystallizes in the monoclinic space group C2/c with Z = 4 in a cell of dimensions a = 14.891 (2), b = 10.780(2), c = 8.769(1) Å, β = 97.47(2)°, V = 1395.7(7) Å3 has crystallographic twofold symmetry. The E form crystallizes in the orthorhombic space group Pbca with a = 11.730(1), b = 6.932(1), c = 16.841(1) Å, V = 1369.4(2) Å3 and Z = 4. Its molecules have crystallographically dictated [Formula: see text] symmetry. In both isomers the phenyl rings are roughly perpendicular to the average ethylene plane. The atoms characterizing this plane show significant deviations from planarity in the Z isomer. Marked bond-angle distortions at the ethene carbons of both structures are observed. The 1H and 13C NMR spectra of the compounds were measured and, particularly in the case of the 1H chemical shifts, fall into two quite separate spectral regions. At low temperature, two conformational isomers, those with different relative orientation of the C—Cl bonds of the phenyl rings, are observed in the spectrum of each compound. Keywords: chlorostilbenes, overcrowded molecules. X-ray structure, conformations, NMR spectroscopy.

scholarly journals 1H-NMR characterization of l-tryptophan binding to TRAP, the trp RNA-binding attenuation protein of Bacillus subtilis

1996 ◽  
Vol 315 (3) ◽  
pp. 895-900 ◽  
Author(s):  
Vasudevan RAMESH ◽  
Tom BROWN
Keyword(s):  
Bacillus Subtilis ◽  
Complex Formation ◽  
1H Nmr ◽  
Rna Binding ◽  
Chemical Exchange ◽  
Chemical Shifts ◽  
Large Change ◽  
Binding Pocket ◽  
Nmr Study ◽  
Nmr Characterization

A 1H-NMR study of the binding of L-tryptophan to the trp RNA-binding attenuation protein of Bacillus subtilis (TRAP), an ondecamer (91.6 kDa), has been implemented. The assignment of the aromatic indole ring proton resonances of the bound tryptophan ligand has been successfully carried out by two-dimensional chemical exchange experiments. The observation of only a single set of chemical shifts of the bound ligand demonstrates that the tryptophan binding site is identical in all the 11 subunits of the protein. Further, the large change in ligand chemical shifts suggests that the conformation of tryptophan ligand undergoes a significant rearrangement after complex formation with TRAP. This is further substantiated by the extensive ligand-induced chemical shift changes observed to the protein resonances and identification of several strong ligand–protein intermolecular nuclear Overhauser effects. A correlation of these preliminary NMR data with the X-ray crystal structure of the TRAP–tryptophan complex also suggests, tentatively, that the observed changes to the NMR spectra of the protein might correspond to changes associated with residues surrounding the tryptophan binding pocket owing to complex formation.

Variable temperature 13C NMR study of some L(CO)3FeH(SiR3) (L = CO, P(OPh)3; R = Ph, Me, Cl) species. X-ray crystal structure of P(OPh)3(CO)3Fe(H)SiPh3

Polyhedron ◽  
1991 ◽  
Vol 10 (8) ◽  
pp. 841-849 ◽  
Author(s):  
John W. Connolly ◽  
Michael J. Hatlee ◽  
Alan H. Cowley ◽  
Paul R. Sharp
Keyword(s):  
Crystal Structure ◽  
13C Nmr ◽  
Variable Temperature ◽  
X Ray ◽  
Nmr Study

Crystal Structure and NMR Study of Tetrakis(acetonitrile)silver(I) Fluorosulfonate [Ag(CH3CN)4]+[SO3F]–

2014 ◽  
Vol 69 (3) ◽  
pp. 373-375 ◽  
Author(s):  
Can-Carlo Dörtbudak ◽  
Karin Lux ◽  
Andreas Kornath
Keyword(s):  
Crystal Structure ◽  
Nmr Spectroscopy ◽  
Title Compound ◽  
Unit Cell ◽  
Fluorosulfonic Acid ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Nmr Study

The title compound [Ag(CH3CN)4]+[SO3F]- crystallizes in the orthorhombic space group Pna21, a = 24:383(24), b = 8:632(11), c = 20:755(17) Å, V = 4368(6) Å3, Z = 12, with three independent formula units in the unit cell. A comparison with the isostructural compound [Ag(CH3CN)4]+ [ClO4]- is given. The salt has also been characterized by solution 1H and 19F NMR spectroscopy and the data compared to that of fluorosulfonic acid

Synthesis, NMR and ultraviolet spectroscopy of [10] (N6,9)-6-aminopurinophane; calculation of the chemical shifts in the [n](N6,9)-6-aminopurinophane series

1995 ◽  
Vol 73 (12) ◽  
pp. 2224-2232 ◽  
Author(s):  
Alfredo Capretta ◽  
Russell A. Bell
Keyword(s):  
Chemical Shifts ◽  
Variable Temperature ◽  
Bathochromic Shift ◽  
Ultraviolet Spectroscopy ◽  
Methylene Bridge ◽  
Nmr Study ◽  
Complete Assignment ◽  
Subsequent Cyclization ◽  
Semi Empirical ◽  
Hypochromic Effect

[10](N6,9)-6-Aminopurinophane was prepared via a Mitsunobu reaction involving 6-chloropurine and 10-azido-1-decanol. Reduction of the azido moiety to an amine allowed for subsequent cyclization to the cyclophane. N6-Nonyladenine, 9-nonyladenine, and N6,9-dinonyladenine were also prepared using the established chemistry. Heating the [10](N6,9)-6-aminopurinophane to 90 °C allowed for a complete assignment of the proton and carbon spectra, while cooling the sample to −77 °C revealed additional isomers likely due to the anti–syn isomerization about the N6—C6 bond. A variable temperature proton NMR study revealed a ΔGc≠ of 59.4 ± 5.5 kJ mol−1 associated with the interchange between the two major conformers. The ultraviolet spectra of the [n](N6,9)-6-aminopurinophane series show a bathochromic shift and a hypochromic effect in the transitions as the methylene chain length decreases (i.e., n = 10 to 9 to 8). The aminopurinophanes are used to assess the relative merits of a semi-empirical model that allows for the calculation of the chemical shifts of the methylene bridge protons. Keywords: synthesis of heterocyclophanes, variable temperature NMR, cyclophane conformational analysis, ultraviolet spectroscopy, calculation of chemical shift.

Characterization and nonrigid behaviour of a carboxylate-bridged rhodium dimer

1994 ◽  
Vol 72 (5) ◽  
pp. 1294-1301 ◽  
Author(s):  
William R. Cullen ◽  
Steven J. Rettig ◽  
Eugene B. Wickenheiser
Keyword(s):  
Crystal Structure ◽  
Least Squares ◽  
Variable Temperature ◽  
Heavy Atom ◽  
Molecular Rearrangement ◽  
Full Matrix ◽  
Space Group ◽  
H Nmr ◽  
Nmr Data ◽  
Nmr Study

Bis(μ-t-butylacetato)bis(norbornadiene)dirhodium(I) 1 is prepared by a reaction between pivaloyl camphor and (norbornadiene)rhodium(I) chloride dimer. A molecular rearrangement takes place in which the pivaloyl groups of the pivaloyl camphor starting material are incorporated into the end product as bridging t-butylcarboxylate ligands. A variable temperature 1H NMR study and corresponding dynamic computer fit of the NMR data, and crystal structure are reported for the structurally nonrigid dimer. Crystals of 1 are triclinic, a = 10.454(1), b = 10.817(1), c = 12.424(1) Å, α = 64.904(7), β = 100.320(7), γ = 109.382(8)°, Z = 2, space group [Formula: see text] The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.070 and Rw = 0.081 for 3093 reflections with I ≥ 3σ(I).

Sign in / Sign up

Export Citation Format

Share Document