scholarly journals Hydrogen atoms in bridging positions from quantum crystallographic refinements: influence of hydrogen atom displacement parameters on geometry and electron density

CrystEngComm ◽  
2020 ◽  
Vol 22 (28) ◽  
pp. 4778-4789 ◽  
Author(s):  
Lorraine A. Malaspina ◽  
Anna A. Hoser ◽  
Alison J. Edwards ◽  
Magdalena Woińska ◽  
Michael J. Turner ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Electron Density ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Atom Displacement

Hydrogen atom positions can be obtained accurately from X-ray diffraction data of hydrogen maleate salts via Hirshfeld atom refinement.

SHADEweb server for estimation of hydrogen anisotropic displacement parameters

2006 ◽  
Vol 39 (5) ◽  
pp. 757-758 ◽  
Author(s):  
Anders Østergaard Madsen
Keyword(s):  
Hydrogen Atom ◽  
Neutron Diffraction ◽  
Electron Density ◽  
Atomic Motion ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Reference Models ◽  
Anisotropic Displacement Parameters ◽  
Advanced Applications

TheSHADEweb server estimates anisotropic displacement parameters for hydrogen atoms by combining a rigid-body analysis of the non-hydrogen-atom anisotropic displacement parameters (ADPs) with a contribution from internal atomic motion. The contributions from internal mean square displacements are based on a previously compiled database derived from analysis of neutron diffraction experiments. The estimated hydrogen-atom ADPs can be used as fixed parameters in advanced applications of high-resolution X-ray diffraction, such as electron density studies using multipole modelling. The resulting electron density models have been shown to be in excellent agreement with reference models based on atomic motion derived from neutron diffraction experiments.

scholarly journals Hirshfeld atom refinement

IUCrJ ◽  
2014 ◽  
Vol 1 (5) ◽  
pp. 361-379 ◽  
Author(s):  
Silvia C. Capelli ◽  
Hans-Beat Bürgi ◽  
Birger Dittrich ◽  
Simon Grabowsky ◽  
Dylan Jayatilaka
Keyword(s):  
Hydrogen Atom ◽  
Diffraction Data ◽  
Iterative Procedure ◽  
Structural Parameters ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
Electron Densities ◽  
X Ray ◽  
Bond Lengths ◽  
Better Than

Hirshfeld atom refinement (HAR) is a method which determines structural parameters from single-crystal X-ray diffraction data by using an aspherical atom partitioning of tailor-madeab initioquantum mechanical molecular electron densities without any further approximation. Here the original HAR method is extended by implementing an iterative procedure of successive cycles of electron density calculations, Hirshfeld atom scattering factor calculations and structural least-squares refinements, repeated until convergence. The importance of this iterative procedure is illustratedviathe example of crystalline ammonia. The new HAR method is then applied to X-ray diffraction data of the dipeptide Gly–L-Ala measured at 12, 50, 100, 150, 220 and 295 K, using Hartree–Fock and BLYP density functional theory electron densities and three different basis sets. All positions and anisotropic displacement parameters (ADPs) are freely refined without constraints or restraints – even those for hydrogen atoms. The results are systematically compared with those from neutron diffraction experiments at the temperatures 12, 50, 150 and 295 K. Although non-hydrogen-atom ADPs differ by up to three combined standard uncertainties (csu's), all other structural parameters agree within less than 2 csu's. Using our best calculations (BLYP/cc-pVTZ, recommended for organic molecules), the accuracy of determining bond lengths involving hydrogen atoms from HAR is better than 0.009 Å for temperatures of 150 K or below; for hydrogen-atom ADPs it is better than 0.006 Å2as judged from the mean absolute X-ray minus neutron differences. These results are among the best ever obtained. Remarkably, the precision of determining bond lengths and ADPs for the hydrogen atoms from the HAR procedure is comparable with that from the neutron measurements – an outcome which is obtained with a routinely achievable resolution of the X-ray data of 0.65 Å.

scholarly journals Crystallographic features of ammonium fluoroelpasolites: dynamic orientational disorder in crystals of (NH4)3HfF7 and (NH4)3Ti(O2)F5

2017 ◽  
Vol 73 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Anatoly A. Udovenko ◽  
Alexander A. Karabtsov ◽  
Natalia M. Laptash
Keyword(s):  
Single Crystal ◽  
Electron Density ◽  
Diffraction Data ◽  
Central Atom ◽  
X Ray Diffraction ◽  
Dynamic Nature ◽  
Orientational Disorder ◽  
High Quality ◽  
Structural Units ◽  
X Ray

A classical elpasolite-type structure is considered with respect to dynamically disordered ammonium fluoro-(oxofluoro-)metallates. Single-crystal X-ray diffraction data from high quality (NH4)3HfF7 and (NH4)3Ti(O2)F5 samples enabled the refinement of the ligand and cationic positions in the cubic Fm \bar 3 m (Z = 4) structure. Electron-density atomic profiles show that the ligand atoms are distributed in a mixed (split) position instead of 24e. One of the ammonium groups is disordered near 8c so that its central atom (N1) forms a tetrahedron with vertexes in 32f. However, a center of another group (N2) remains in the 4b site, whereas its H atoms (H2) occupy the 96k positions instead of 24e and, together with the H3 atom in the 32f position, they form eight spatial orientations of the ammonium group. It is a common feature of all ammonium fluoroelpasolites with orientational disorder of structural units of a dynamic nature.

The first proof of protonated anion tetrahedra in the tsumcorite-type compounds

2004 ◽  
Vol 68 (5) ◽  
pp. 757-767 ◽  
Author(s):  
T. Mihajlović ◽  
H. Effenberger
Keyword(s):  
Crystal Structure ◽  
Hydrothermal Synthesis ◽  
Single Crystal ◽  
Diffraction Data ◽  
Title Compound ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
Synthetic Compounds ◽  
X Ray

AbstractHydrothermal synthesis produced the new compound SrCo2(AsO4)(AsO3OH)(OH)(H2O). The compound belongs to the tsumcorite group (natural and synthetic compounds with the general formula M(1)M(2)2(XO4)2(H2O,OH)2; M(1)1+,2+,3+ = Na, K, Rb, Ag, NH4, Ca, Pb, Bi, Tl; M(2)2+,3+ = Al, Mn3+, Fe3+, Co, Ni, Cu, Zn; and X5+,6+ = P, As, V, S, Se, Mo). It represents (1) the first Sr member, (2) the until now unknown [7]-coordination for the M(1) position, (3) the first proof of (partially) protonated arsenate groups in this group of compounds, and (4) a new structure variant.The crystal structure of the title compound was determined using single-crystal X-ray diffraction data. The compound is monoclinic, space group P21/a, with a = 9.139(2), b = 12.829(3), c = 7.522(2) Å, β = 114.33(3)°, V = 803.6(3) Å3, Z = 4 [wR2 = 0.065 for 3530 unique reflections]. The hydrogen atoms were located experimentally.

Experimental electron density study of 1,2,4-triazole at 15 K. A comparison with ab initio-calculations

1997 ◽  
Vol 212 (3) ◽  
Author(s):  
P. Fuhrmann ◽  
T. Koritsánszky ◽  
P. Luger
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electron Density ◽  
Diffraction Data ◽  
Topological Properties ◽  
X Ray Diffraction ◽  
X Ray ◽  
Experimental Electron Density ◽  
Density Study

AbstractTopological properties and the Laplacian function of the electron density of 1,2,4-triazole have been determined from X-ray diffraction data collected at 15 K. 1,2,4-Triazole, C

Electron-density Fourier maps of an untwinnedYBa2Cu3O6.877single crystal by x-ray-diffraction data

1993 ◽  
Vol 48 (14) ◽  
pp. 10638-10641 ◽  
Author(s):  
J. D. Sullivan ◽  
P. Bordet ◽  
M. Marezio ◽  
K. Takenaka ◽  
S. Uchida
Keyword(s):  
Electron Density ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
X Ray

scholarly journals Diamonds in the rough: a strong case for the inclusion of weak-intensity X-ray diffraction data

2014 ◽  
Vol 70 (5) ◽  
pp. 1491-1497 ◽  
Author(s):  
Jimin Wang ◽  
Richard A. Wing
Keyword(s):  
Electron Density ◽  
Diffraction Data ◽  
Heavy Atom ◽  
Uniform Density ◽  
X Ray Diffraction ◽  
X Ray ◽  
Density Correlation ◽  
Atomic Models ◽  
Weak Intensity

Overwhelming evidence exists to show that the inclusion of weak-intensity, high-resolution X-ray diffraction data helps improve the refinement of atomic models by imposing strong constraints on individual and overall temperatureBfactors and thus the quality of crystal structures. Some researchers consider these data to be of little value and opt to discard them during data processing, particularly at medium and low resolution, at which individualBfactors of atomic models cannot be refined. Here, new evidence is provided to show that the inclusion of these data helps to improve the quality of experimental phases by imposing proper constraints on electron-density models during noncrystallographic symmetry (NCS) averaging. Using electron-density correlation coefficients as criteria, the resolution of data has successfully been extended from 3.1 to 2.5 Å resolution with redundancy-independent mergingRfactors from below 100% to about 310%. It is further demonstrated that phase information can be fully extracted from observed amplitudes throughde novoNCS averaging. Averaging starts with uniform density inside double-shelled spherical masks and NCS matrices that are derived from bound heavy-atom clusters at the vertices of cuboctahedrally symmetric protein particles.

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