scholarly journals Tracing electron density changes in langbeinite under pressure

IUCrJ ◽  
2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Roman Gajda ◽  
Dongzhou Zhang ◽  
Jan Parafiniuk ◽  
Przemysław Dera ◽  
Krzysztof Woźniak
Keyword(s):  
Electron Density ◽  
Theoretical Calculations ◽  
Ambient Pressure ◽  
Detailed Examination ◽  
Thermal Parameters ◽  
Electron Density Redistribution ◽  
Cubic System ◽  
Chemical Behaviour ◽  
Compression Effects ◽  
External Stimuli

Pressure is well known to dramatically alter physical properties and chemical behaviour of materials, much of which is due to the changes in chemical bonding that accompany compression. Though it is relatively easy to comprehend this correlation in the discontinuous compression regime, where phase transformations take place, understanding of the more subtle continuous compression effects is a far greater challenge, requiring insight into the finest details of electron density redistribution. In this study, a detailed examination of quantitative electron density redistribution in the mineral langbeinite was conducted at high pressure. Langbeinite is a potassium magnesium sulfate mineral with the chemical formula [K2Mg2(SO4)3], and crystallizes in the isometric tetartoidal (cubic) system. The mineral is an ore of potassium, occurs in marine evaporite deposits in association with carnallite, halite and sylvite, and gives its name to the langbeinites, a family of substances with the same cubic structure, a tetrahedral anion, and large and small cations. Single-crystal X-ray diffraction data for langbeinite have been collected at ambient pressure and at 1 GPa using a combination of in-house and synchrotron techniques. Experiments were complemented by theoretical calculations within the pressure range up to 40 GPa. On the basis of changes in structural and thermal parameters, all ions in the langbeinite structure can be grouped into `soft' (potassium cations and oxygens) and `hard' (sulfur and magnesium). This analysis emphasizes the importance of atomic basins as a convenient tool to analyse the redistribution of electron density under external stimuli such as pressure or temperature. Gradual reduction of completeness of experimental data accompanying compression did not significantly reduce the quality of structural, electronic and thermal parameters obtained in experimental quantitative charge density analysis.

X-ray investigation of electron density redistribution on complexation

1991 ◽  
Vol 251 ◽  
pp. 11-27 ◽  
Author(s):  
G.N. Dolenko ◽  
A.L. Litvin ◽  
V.P. Elin ◽  
O.Kh. Poleshchuk
Keyword(s):  
Electron Density ◽  
Electron Density Redistribution ◽  
X Ray

scholarly journals ELECTRON DENSITY STUDIES ON THE REGIOSELECTIVITY OF DEPROTONATION REACTIONS

2014 ◽  
Vol 70 (a1) ◽  
pp. C287-C287
Author(s):  
Juan Van der Maelen ◽  
Javier Cabeza
Keyword(s):  
Electron Density ◽  
Theoretical Calculations ◽  
Density Ratio ◽  
Atomic Charge ◽  
Heterocyclic Ring ◽  
Bond Critical Point ◽  
Electron Densities ◽  
Total Energy Density ◽  
Topological Parameters ◽  
Alkyl Groups

The C-alkyl groups of cationic triruthenium cluster complexes of the type [Ru3(µ-H)(µ-κ2N1,C2-EtnMemPyHk)(CO)10]+ (EtnMemPyHk represents a generic C-alkyl-N-methyl-pyrazium species) have been deprotonated to give kinetic products that contain unprecedented C-alkylidene derivatives and maintain the original edge-bridged decacarbonyl structure. When the starting complexes contain various C-alkyl groups, the selectivity of these deprotonation reactions is related to the atomic charges of the alkyl H atoms, as suggested by DFT/natural-bond orbital (NBO) calculations. Three additional electronic properties of the C-alkyl C-H bonds have also been found to correlate with the experimental regioselectivity since, in all cases, the deprotonated C-H bond has the smallest electron density at the bond critical point (bcp), the greatest Laplacian of the electron density at the bcp, and the greatest total energy density ratio at the bcp (computed by using the quantum theory of atoms in molecules, QTAIM). The kinetic decacarbonyl products evolve, under appropriate reaction conditions that depend upon the position of the C-alkylidene group in the heterocyclic ring, towards face-capped nonacarbonyl derivatives (thermodynamic products). Theoretical calculations support the proposal that the selectivity of these deprotonation reactions is primarily determined by the atomic charge of the alkyl H atoms: the higher the charge the easier the deprotonation when the starting complexes contain various C-alkyl groups. On the other hand, although QTAIM results have been obtained here only from theoretical electron densities for the above clusters, comparisons with local and integral topological parameters derived from both experimental and theoretical electron densities for the related triruthenium complex [Ru3(μ-H)2(μ3-MeImCH)(CO)9] (Me2Im = 1,3-dimethylimidazol-2-ylidene) may easily be made.

Topological characterization of electron density, electrostatic potential and intermolecular interactions of 2-nitroimidazole: an experimental and theoretical study

2016 ◽  
Vol 72 (5) ◽  
pp. 775-786 ◽  
Author(s):  
Chinnasamy Kalaiarasi ◽  
Mysore S Pavan ◽  
Poomani Kumaradhas
Keyword(s):  
Electron Density ◽  
Intermolecular Interactions ◽  
Electrostatic Potential ◽  
Theoretical Calculations ◽  
Topological Analysis ◽  
X Ray Diffraction ◽  
Topological Characterization ◽  
Data Set ◽  
X Ray ◽  
Charge Concentration

An experimental charge density distribution of 2-nitroimidazole was determined from high-resolution X-ray diffraction and the Hansen–Coppens multipole model. The 2-nitroimidazole compound was crystallized and a high-angle X-ray diffraction intensity data set has been collected at low temperature (110 K). The structure was solved and further, an aspherical multipole model refinement was performed up to octapole level; the results were used to determine the structure, bond topological and electrostatic properties of the molecule. In the crystal, the molecule exhibits a planar structure and forms weak and strong intermolecular hydrogen-bonding interactions with the neighbouring molecules. The Hirshfeld surface of the molecule was plotted, which explores different types of intermolecular interactions and their strength. The topological analysis of electron density at the bond critical points (b.c.p.) of the molecule was performed, from that the electron density ρbcp(r) and the Laplacian of electron density ∇2ρbcp(r) at the b.c.p.s of the molecule have been determined; these parameters show the charge concentration/depletion of the nitroimidazole bonds in the crystal. The electrostatic parameters like atomic charges and the dipole moment of the molecule were calculated. The electrostatic potential surface of the molecule has been plotted, and it displays a large electronegative region around the nitro group. All the experimental results were compared with the corresponding theoretical calculations performed usingCRYSTAL09.

scholarly journals Crystal structures and dynamical properties of dense CO2

2016 ◽  
Vol 113 (40) ◽  
pp. 11110-11115 ◽  
Author(s):  
Xue Yong ◽  
Hanyu Liu ◽  
Min Wu ◽  
Yansun Yao ◽  
John S. Tse ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Theoretical Calculations ◽  
Ambient Pressure ◽  
Md Simulations ◽  
Ab Initio Molecular Dynamics ◽  
Structural Polymorphism ◽  
Stability Structure ◽  
Dynamical Properties ◽  
The Stability

Structural polymorphism in dense carbon dioxide (CO2) has attracted significant attention in high-pressure physics and chemistry for the past two decades. Here, we have performed high-pressure experiments and first-principles theoretical calculations to investigate the stability, structure, and dynamical properties of dense CO2. We found evidence that CO2-V with the 4-coordinated extended structure can be quenched to ambient pressure below 200 K—the melting temperature of CO2-I. CO2-V is a fully coordinated structure formed from a molecular solid at high pressure and recovered at ambient pressure. Apart from confirming the metastability of CO2-V (I-42d) at ambient pressure at low temperature, results of ab initio molecular dynamics and metadynamics (MD) simulations provided insights into the transformation processes and structural relationship from the molecular to the extended phases. In addition, the simulation also predicted a phase V′(Pna21) in the stability region of CO2-V with a diffraction pattern similar to that previously assigned to the CO2-V (P212121) structure. Both CO2-V and -V′ are predicted to be recoverable and hard with a Vicker hardness of ∼20 GPa. Significantly, MD simulations found that the CO2 in phase IV exhibits large-amplitude bending motions at finite temperatures and high pressures. This finding helps to explain the discrepancy between earlier predicted static structures and experiments. MD simulations clearly indicate temperature effects are critical to understanding the high-pressure behaviors of dense CO2 structures—highlighting the significance of chemical kinetics associated with the transformations.

scholarly journals Charge-density studies of energetic materials: CL-20 and FOX-7

2008 ◽  
Vol 64 (1) ◽  
pp. 42-49 ◽  
Author(s):  
A. Meents ◽  
B. Dittrich ◽  
S. K. J. Johnas ◽  
V. Thome ◽  
E. F. Weckert
Keyword(s):  
Electron Density ◽  
Energetic Materials ◽  
Theoretical Calculations ◽  
Topological Analysis ◽  
Single Crystal Diffraction ◽  
Figures Of Merit ◽  
Hartree Fock ◽  
Structure Factors ◽  
Derived Properties ◽  
Impact Sensitivities

Experimental electron densities and derived properties have been determined for the two energetic materials CL-20 (3,5,9,11-tetraacetyl-14-oxo-1,3,5,7,9,11-hexaazapentacyclo-[5.5.3.02,6.04,10.08,12]pentadecane), and FOX-7 (1,1-diamino-2,2-dinitroethylene) from single-crystal diffraction. Synchrotron data extending to high scattering angles were measured at low temperature. Low figures-of-merit and excellent residuals were obtained. The Hansen & Coppens multipole-model electron density was compared with results from theoretical calculations via structure factors simulating an experiment. Chemical bonding in the molecules is discussed and a topological analysis gives insight especially into the character of those bonds that are thought to play a key role in the decomposition of the molecules. A comparison of theoretical and experimental electrostatic potentials shows no obvious evidence supporting earlier findings on other nitroheterocyclic molecules that electron-density maxima near the C—NO2 bonds mapped on the electron-density isosurface can be correlated with impact sensitivities. For FOX-7 periodic Hartree–Fock calculations were performed to investigate the influence of the crystal field on the electron density distribution.

A First Experimental Electron Density Study on a C70 Fullerene: (C70C2F5)10

2010 ◽  
Vol 65 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Roman Kalinowski ◽  
Manuela Weber ◽  
Sergey I. Troyanov ◽  
Carsten Paulmann ◽  
Peter Luger
Keyword(s):  
High Resolution ◽  
Electron Density ◽  
Theoretical Calculations ◽  
Asymmetric Unit ◽  
Data Set ◽  
X Ray ◽  
Atomic Properties ◽  
Density Methods ◽  
Experimental Electron Density ◽  
Density Study

The electron density of the C70 fullerene C70(C2F5)10 was determined from a high-resolution X-ray data set measured with synchrotron radiation (beamline F1 of Hasylab/DESY, Germany) at a temperature of 100 K. With 140 atoms in the asymmetric unit this fullerene belongs to the largest problems examined until now by electron density methods. Using the QTAIM formalism quantitative bond topological and atomic properties have been derived and compared with the results of theoretical calculations on the title compound and on free C70

Electron Density Redistribution Accounts for Half the Cooperativity of α Helix Formation

2006 ◽  
Vol 110 (10) ◽  
pp. 4503-4505 ◽  
Author(s):  
Alexandre V. Morozov ◽  
Kiril Tsemekhman ◽  
David Baker
Keyword(s):  
Electron Density ◽  
Electron Density Redistribution ◽  
Helix Formation ◽  
Α Helix
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