Crystal Structure and Charge Distribution of Pyrazine: Effects of Extinction, Thermal Diffuse Scattering and Series Termination* BY G. DE WITH, S. HARKEMA AND D. FEIL
نویسندگان
چکیده
The crystal structure and electronic charge distribution of pyrazine (1,4-diazabenzene) has been determined at 184 K by X-ray methods. The structural results of Wheatley [Acta Cryst. (1957), 10, 182-187] have been confirmed. A clear indication of bonding effects is obtained. Neither positional and thermal parameters nor difference-Fourier maps are affected by extinction. The effect of thermal diffuse scattering (TDS) on positional parameters is also negligible. However, after correction for TDS, thermal parameters increase significantly. The difference-Fourier map is influenced by TDS as well as the inclusion of high-order Fourier terms.
منابع مشابه
Molecular-Dynamics Simulation of Crystalline 18-Crown-6:* Thermal Shortening of Covalent Bonds
Molecular-dynamics simulations of crystalline 18crown-6 have been performed in a study of the apparent thermal shortening of covalent bonds observed in crystal structures. At 100 K, a shortening of 0.006 _+ 0.001 A for C----C and C----O bonds was obtained. This result was found to be independent of details of the force field and the simulation. There was agreement between computational and expe...
متن کاملPotential of Mean Force by Thermodynamic Integration: Molecular-dynamics Simulation of Decomplexation
“Umbrella samplmg” has been incorporated in the thermodynamic integration method to obtain a potential of mean force by slow growth molecular-dynamics simulations. The method was tested for liquid argon, for which good agreement was obtained with a standard potential of mean force, as derived from the radial pair-correlation function. For a sodium chloride ion-pair in aqueous solution the calcu...
متن کاملMolecular dynamics of 18-crown-6 complexes with alkali-metal cations and urea: Prediction of their conformations and comparison with data from the cambridge structural database
Complexes of 18-crown-6 with alkali-metal cations (Na', K', and Rb'), urea, and the uncomplexed crown ether were studied in V ~ C U O with the molecular dynamics method. Conformational data from these calculations (simulation times in the range from 6-15 ns) was compared with information from the Cambridge Structural Database. Despite the differences in condition between the simulations and the...
متن کاملAdmixtures to d-wave gap symmetry in untwinned YBa2Cu3O7 superconducting films measured by angle-resolved electron tunneling.
We report on an ab anisotropy of Jc parallel b/Jc parallel a approximately/= 1.8 IcRn parallelb/IcRn parallel a approximately/= 1.2 and in ramp-edge junctions between untwinned YBa2Cu3O7 and s-wave Nb. For these junctions, the angle theta with the YBa2Cu3O7 crystal b axis is varied as a single parameter. The RnA(theta) dependence presents twofold symmetry. The minima in IcRn at theta approximat...
متن کاملA prospective, multicenter, phase I matched-comparison group trial of safety, pharmacokinetics, and preliminary efficacy of riluzole in patients with traumatic spinal cord injury.
A prospective, multicenter phase I trial was undertaken by the North American Clinical Trials Network (NACTN) to investigate the pharmacokinetics and safety of, as well as obtain pilot data on, the effects of riluzole on neurological outcome in acute spinal cord injury (SCI). Thirty-six patients, with ASIA impairment grades A-C (28 cervical and 8 thoracic) were enrolled at 6 NACTN sites between...
متن کامل