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showing 10 items of 2807 documents
Mono- and di-bridged heterobimetallic systems from group 5 hydride phosphido and hydride phosphino metalloligands. Crystal structure of Cp2Ta(H)( μ-H…
1997
Abstract The trihydrides Cp2MH3 (M Nb, Ta) react with chlorophosphines PR2Cl (R Me, Ph) affording phosphonium salts [Cp2MH2(PR2H)]+, Cl− (2 (a, b) 2′ (a, b)). Depending on the metal (Nb or Ta) and on the nature of the phosphine substituent (Me or Ph), deprotonation of these salts leads to hydride phosphino Cp2MH(PR2H) (3 (a, b) 3′a) or hydrided phosphido Cp2 TaH2(PPh2) (4′b) metalloligands. These two kinds of complexes are able to bind [M′(CO)5] or [M′(CO)4] (M′ Cr, Mo, W) organometallic fragments to give mono- or di-bridged heterobimetallic systems. The crystallographic analysis of Cp2Ta(H)(μ-H)(μ-PMe2)Cr(CO)4 (7′aCr) is reported and discussed.
A second monoclinic polymorph of 2-(3,5-dimethyl-1H-pyrazol-1-yl)-2-hy-droxy-imino-N'-[1-(pyridin-2-yl)ethyl-idene]acetohydrazide.
2013
The title compound, C14H16N6O2, is a second monoclinic polymorph of 2-[1-(3,5-dimethyl)pyrazolyl]-2-hydroxyimino-N′-[1-(2-pyridyl)ethylidene] acetohydrazide, with two crystallographically independent molecules per asymmetric unit. The non-planar molecules are chemically equal having similar geometric parameters. The previously reported polymorph [Plutenko et al. (2012 ▶). Acta Cryst. E68, o3281] was described in space group Cc (Z = 4). The oxime group and the O atom of the amide group are anti with respect to the C—C bond. In the crystal, molecules are connected by N—H⋯N hydrogen bonds into zigzag chains extending along the b axis.
PyridiniumD(+)-10-camphorsulfonate hemihydrate
2002
In the crystal structure of pyridinium d(+)-10-camphorsulfonate hemihydrate, C5H6N+·C10H15O4S−·0.5H2O, a water molecule lying on a twofold axis serves as a donor of two hydrogen bonds, thus linking two camphorsulfonate anions. Each anion in its turn acts as a hydrogen-bond acceptor for the NH group of a pyridinium cation.
The crystal structure of 3,5-diisopropyl-4-nitropyrazole from X-ray powder diffraction data
2001
The crystal structure of 3,5-diisopropyl-4-nitropyrazole, 3c, has been determined by a Patterson Search method from laboratory X-ray powder diffraction data. The crystal data are: monoclinic symmetry with the unit-cell parameters aa 19:530O5U; ba 6:485O1U and ca 17:937O3U A; ba 100:32O1U8; space group I2/a ,C 9H15N3O2, Za 8, 293 K. After indexing the powder pattern by two methods, the unit-cell parameters found were refined by a least-squares technique. A whole pattern- fitting program was used to extract the integrated intensities. The structure was solved taking a related compound as a search model and the final Rietveld refinement converged to Rwpa 0.1971 and Rpa 0.1437. The structure pr…
rac-Ethyl (2Z)-3-{2-[(Z)-4-ethoxy-4-oxobut-2-en-2-ylamino]cyclohexylamino}but-2-enoate
2011
The asymmetric unit of the title compound, C18H30N2O4, contains two independent molecules. In each molecule, the cyclohexane ring adopts a chair conformation with equatorial orientation of the substituents, and the conformation is stabilized by two intramolecular N—H...O hydrogen bonds, forming rings of S(6) graph-set motif. One ethoxy group and one ethyl group are disordered over two sets of sites with refined occupancy ratios of 0.704 (2):0.296 (2) and 0.505 (3):0.495 (3), respectively. In the crystal, a weak intermolecular C—H...O hydrogen interaction is observed, involving the O atom of the major component of the disordered eth…
N-(3-Methoxypropyl)-1,8-naphthalimide
2003
In the title compound, C16H15NO3, the 1,8-naphthalenodicarboximide group is nearly planar and, in the naphthalimide ring system, the characteristic alternating pattern of bond lengths is observed. In the crystal, the molecules are connected by a weak C—H⋯O hydrogen bond and extend in the direction parallel to the b axis.
1,4-Dihydro-1-methyl-4-nitriminopyridine Dihydrate
1998
Molecules of the title compound, C6H7N302.2H20, are almost planar with the NNO2 nitrimino group twisted 8 (1) ° out of the plane of the pyridine ring. The nitrimino group and CsN ring form a conju- gated 7r-electron system. These molecules together with water molecules are arranged in planes, They are con- nected with each other by O--H.-.O, O--H...N and weaker C--H..-O hydrogen bonds. Four water mol- ecules form a planar square (OH..-O--H)2 ring with O-..O distances equal to 2.741 (2) and 2.778(2)A. These rings join pairs of molecular planes into double layers, interacting otherwise by van der Waals forces.
1,5-Dimethyl-2-nitrimino-1,2-dihydropyridine
2006
Methylation of 5-methyl-2-nitraminopyridine provides the title compound, C7H9N3O2, as the only product. The molecule consists of two planar fragments, viz. an aromatic ring and a nitrimino substituent. The NNO2 group is twisted by 17 (2)° out of the plane of the pyridine ring. Despite a small torsion angle between these fragments, the geometry of the molecule indicates the participation of the π-electrons in the C—N bond. The hydrogen bonds in the crystal structure seem to be too weak to generate any deformations observed in the molecule.
Ab initio study of the internal rotation potential of p-disilanylbenzene and p-(1,1′,2,2′-tetramethyldisilanyl)benzene
1996
Abstract We present a detailed ab initio study of the geometrical structure and torsional potential of p -disilanylbenzene and its methyl derivative p -(1,1′,2,2′-tetramethyldisilanyl)benzene. The geometries of the different conformers have been fully optimized at the Hartree-Fock 3-21G ∗ and 6-31G ∗ levels. In all cases, the most stable conformation corresponds to the conformer in which the phenylene group lies in a plane perpendicular to the four silicon atoms. The torsional potential curves calculated using the 3-21G ∗ and 6-31G ∗ basis sets show similar features. In the case of p -(1,1′,2,2′-tetramethyldisilanyl)benzene the interactions between the hydrogen atoms of phenylene and the me…
Improvement of FAO-56 Model to Estimate Transpiration Fluxes of Drought Tolerant Crops under Soil Water Deficit: Application for Olive Groves
2014
[EN] Agro-hydrological models are considered an economic and simple tool for quantifying crop water requirements. In the last two decades, agro-hydrological physically based models have been developed to simulate mass and energy exchange processes in the soil-plant-atmosphere system. Although very reliable, because of the high number of required variables, simplified models have been proposed to quantify crop water consumes. The main aim of this paper is to propose an amendment of the Food and Agricultural Organization (FAO) of the United Nations FAO-56 spreadsheet program to introduce a more realistic shape of the stress function, valid for mature olive orchards (Olea europaea L.). The mod…