1,721,103 research outputs found
Crystal structure of 2,5,6-trimethyl-9-methoxy-4H-pyrrolo[3,2,1-ij ] quinolin-4-one
No full textA pale-yellow crystal of parallelepiped habit, produced by crystallization from methanol and having approximate dimensions of 0.2, 0.2, 0.8 mm, was selected for X-ray work. Intensity data were collected using a Siemens-Nicolet R3m/V automated diffractometer and highly oriented graphite crystal monochromatized Mo Ka radiation (fine tube, 50 KV, 30 mA, lambda = 0.71073 À). The X-rays diffracted from the crystal were recorded by a Polaroid cassette mounted in front of the detector (at 19.5 cm), and a rotation photograph around the phi axis gave twenty 2X, 2Y values for evaluating the quality of the crystal and calculating angular positions for the reflections; they were centered later with a centering algorithm. An indexing routine, based on forty equivalent reflections in the range 20 < 2theta <40°, selected a unit cell of the tetragonal system, with the dimensions a = 18.821(5), c = 13.882(8) angstrom and V = 4919(4) cubic angstrom The observed volume and density (1.31(1) g cm-3 corresponded to Z = 16, while the reflection conditions were consistent with the space group 141 cd (No. 110)
Ligating ability of 1,1 '-bis(diphenylphosphino)ferrocene: a structural survey (1994-1998)
No full textThis paper outlines the ligating ability of 1,1'-bis(diphenylphosphino) ferrocene. The focus is on the extensive coordination chemistry exhibited by this ligand to transition metals. The structural parameters of mono-, bi- and polynuclear species are reviewed and simple relationships between some of these parameters are reported and discussed. The review mainly covers the X-ray structure determinations published over the 1994-98 period. (C) 2000 Elsevier Science B.V. All rights reserved
Solid-state structure of 2,6-dimethyl-gamma-pyrone
No full text2,6-dimethyl-4H-pyranylidene-4-one, shortly 2,6- dimethyl-y-pyrone, is a widely known chemical reagent used in the synthesis of various heterocycles. A contin uous quest is being carried out in our research group for metal ligands; the title compound was taken for examination due to its ability of coordinating transition elements, in particular lanthanoids
Chimica di Base
No full textIl testo è stato pensato per presentare in forma concisa i concetti fondamentali della chimica
Chimica di Base Seconda Edizione
No full textIl testo aggiornato recepisce i suggerimenti formulati da docenti e studenti ed è integrato da un CD
Crystal structures of a bis(cyclopentadienyl)(Z)-enyne framed manganese(I)-rhenium(I) complex and its [Co2(CO)8] adduct
No full textThe X-ray structural determination of the manganese(I)-rhenium(I) complex [(OC)3Mn{eta-5-C5H4)(Z)CH = CHC = C(eta-5-C5H4)}Re(CO)3] 1 has been carried out. The structural data show that the (Z)-enyne linkage between the two cyclopentadienyl rings, despite the conjugation that would keep the ligand framework coplanar, allows twisting of the two cyclopentadienylmetal units. Because of this characteristic the Mn Re interatomic distance (6.1 angstrom) is much shorter than in similar bis(cyclopentadienyl)-linked heterobimetallic complexes. Reaction of 1 with [Co2(CO)8] affords quantitatively the corresponding dicobalt tetragonal pyramidal adduct [(OC)3Mn{eta-5-C5H4)(Z)CH = CHC-(OC)3Co-Co(CO)3-C-(eta-5-C5H4)}Re(CO)3]2 the X-ray structure of which has been determined. The presence of the dicobalt unit on the triple bond heavily affects the carbon chain connecting the two cyclopentadienyl rings, and the metal centres are at a larger distance than in 1. Crystal data: 1, triclinic, space group P1BAR, a = 6.546(1), b = 11.066(2), c = 13.451 (3) angstrom, alpha = 96.06(2), beta = 100.46(2), gamma = 96.31 (1)-degrees, R(F) = 0.0466, R'(F) = 0.0542 for 2710 observed reflections with F > 4.0-sigma(F); 2, triclinic, space group P1BAR, a = 9.825(3), b = 11.853(4), c = 13.662(3) angstrom, alpha = 109.41 (2), beta = 1 04.36(2), gamma = 99.16(2)-degrees, Z = 2, R(F) = 0.0325, R'(F) = 0.0352 for 5913 observed reflections with F > 4.0-sigma(F)
1-(2-Hydroxy-4,6-dimethylphenyl)-ethanone
No full textIn the crystal of the title compound, C10H12O2, there are two symmetry-independent molecules, which are essentially superimposable. Each molecule exhibits an intramolecular OD H ... O hydrogen bond, with O ... O separations of 2.483 (4) and 2.468 (4) Angstrom
Molecular modeling, theoretical calculations and property evaluation of three muscarinic agonists, X-ray structures of LU 25-109 and WAL 2014
No full textLU 25-109 (II) and WAL 2014 (talsaclidine, III) are two M1 muscarinic agonists chemically related to the natural substance arecoline (I). All these compounds have beneficial effects on memory and cognition in animals and humans, and they have been proposed in the treatment of Alzheimer's disease, but only III will likely find a place in therapy. In this work we have investigated the solid state structures of II and III and the X-ray structures of the two molecules and of the parent compound I have been used to input a series of computational chemistry efforts. In particular, the X-ray geometries have been manipulated to model 20 molecular structures (1-20) which have been submitted to ab initio, semiempirical quantum mechanics and molecular mechanics calculations. The conformational space accessible to the 20 structures has been assessed by means of potential energy maps. The reactivities of 1-20 have been estimated by examining at the graphics terminal the composition and the extension of the frontier orbitals (HOMOs and LUMOs) and of the molecular electrostatic potential. The information obtained has been interpreted to explain the different degrees of activity shown by I-III. Our data indicate that III has better in vivo activity for its intermediate size, less polar surface, conformational rigidity and orientation of reactive domains. (C) 2000 Elsevier Science B.V. All rights reserved
Structural investigation of [H2cyclam] [O3SCF3]2 (cyclam=1,4,8,11-tetraazacyclotetradecane)
No full textThe 14-membered macrocyle 1,4,8,1 1-tetraazacyclotetradecane (cyclam), a weIl-known N4-donor cyclic system, exhibits great flexibility in accommodating a range of host metal ions and five different arrangements of the chiral nitrogen donor centers are possible in the resulting complexes (Lindoy, 1989). For instance, in cis-[CrCl2(cyclam)]+ (House and McKee, 1984) the absolute configuration is of the type (RRRR), in trans-[ReO2(cyclam)]+ (Luna et al., 1992) it is (RSSR), while in cis-[MoCl2(cyclam)]+ (Hyldtoft et al., 1989) it is (RSRR). In order to gain a deeper understanding of the flexibility of cyclam and of its doubly protonated form, H2cyclam2+, we evaluated the energy content of all conformations. In addition, we present the crystal structure of [H2cyclam] [O3SCF3]2 and a comparison with the data found in [H2cyclam] [ClO4]2 (Nave and Truter, 1974) is reported
Crystal structure of 9-methyladeninium nitrate
No full textA X-ray crystal structure determination of the title compound was carried out. A comparison of the relevant bond distances and angles in the ring system with other published structures showed that protonation has an influence on the ring geometry
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