scholarly journals Hydrogenation Properties of LnAl2 (Ln = La, Eu, Yb), LaGa2, LaSi2 and the Crystal Structure of LaGa2H0.71(2)

Crystals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 193 ◽  
Author(s):  
Anton Werwein ◽  
Christopher Benndorf ◽  
Marko Bertmer ◽  
Alexandra Franz ◽  
Oliver Oeckler ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Hydrogen Gas ◽  
Hydrogen Atoms ◽  
Zintl Phases ◽  
Trigonal Bipyramidal ◽  
Transmission Electron ◽  
Hydrogenation Reactions ◽  
Lanthanide Metals

Many Zintl phases take up hydrogen and form hydrides. Hydrogen atoms occupy interstitial sites formed by alkali or alkaline earth metals and / or bind covalently to the polyanions. The latter is the case for polyanionic hydrides like SrTr2H2 (Tr = Al, Ga) with slightly puckered honeycomb-like polyanions decorated with hydrogen atoms. This study addresses the hydrogenation behavior of LnTr2, where the lanthanide metals Ln introduce one additional valence electron. Hydrogenation reactions were performed in autoclaves and followed by thermal analysis up to 5.0 MPa hydrogen gas pressure. Products were analyzed by powder X-ray and neutron diffraction, transmission electron microscopy, and NMR spectroscopy. Phases LnAl2 (Ln = La, Eu, Yb) decompose into binary hydrides and aluminium-rich intermetallics upon hydrogenation, while LaGa2 forms a ternary hydride LaGa2H0.71(2). Hydrogen atoms are statistically distributed over two kinds of trigonal-bipyramidal La3Ga2 interstitials with 67% and 4% occupancy, respectively. Ga-H distances (2.4992(2) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. 2H solid-state NMR spectroscopy and theoretical calculations on Density Functional Theory (DFT) level confirm that LaGa2H0.7 is a typical interstitial metallic hydride.

scholarly journals Size Matters: New Zintl Phase Hydrides of REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) with Large and Small Cations

Crystals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 600
Author(s):  
Werwein ◽  
Hansen ◽  
Kohlmann
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Structural Diversity ◽  
Type Structure ◽  
Zintl Phases ◽  
Structure Form ◽  
Functional Theory ◽  
X Ray ◽  
Hydrogenation Reactions ◽  
Tetrahedral Voids

Many Zintl phases exhibiting a CrB type structure form hydrides. Systematic studies of AeTtHx (Ae = Ca, Sr, Ba; Tt = Si, Ge, Sn), LnTtHx (Ln = La, Nd; Tt = Si, Ge, Sn), and LnGaHx (Ln = Nd, Gd) showed the vast structural diversity of these systems. Hydrogenation reactions on REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) were performed in steel autoclaves under hydrogen pressure up to 5 MPa and temperatures up to 773 K. The products were analyzed by X-ray and neutron powder diffraction. RESi (RE = Y, Er, Tm) form hydrides in the C-LaGeD type. LaGaD1.66 is isostructural to NdGaD1.66 and shows similar electronic features. Ga-D distances (1.987(13) Å and 2.396(9) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. In TmGaD0.93(2) with a distorted CrB type structure deuterium atoms exclusively occupy tetrahedral voids. Theoretical calculations on density functional theory (DFT) level confirm experimental results and suggest metallic properties for the hydrides.

scholarly journals Higher thermoelectric performance of Zintl phases (Eu0.5Yb0.5)1−xCaxMg2Bi2 by band engineering and strain fluctuation

2016 ◽  
Vol 113 (29) ◽  
pp. E4125-E4132 ◽  
Author(s):  
Jing Shuai ◽  
Huiyuan Geng ◽  
Yucheng Lan ◽  
Zhuan Zhu ◽  
Chao Wang ◽  
...  
Keyword(s):  
Density Functional ◽  
Phonon Scattering ◽  
Theoretical Calculations ◽  
Thermoelectric Performance ◽  
Partial Substitution ◽  
Zintl Phases ◽  
Band Engineering ◽  
Transmission Electron ◽  
P Type ◽  
Callaway Model

Complex Zintl phases, especially antimony (Sb)-based YbZn0.4Cd1.6Sb2 with figure-of-merit (ZT) of ∼1.2 at 700 K, are good candidates as thermoelectric materials because of their intrinsic “electron–crystal, phonon–glass” nature. Here, we report the rarely studied p-type bismuth (Bi)-based Zintl phases (Ca,Yb,Eu)Mg2Bi2 with a record thermoelectric performance. Phase-pure EuMg2Bi2 is successfully prepared with suppressed bipolar effect to reach ZT ∼ 1. Further partial substitution of Eu by Ca and Yb enhanced ZT to ∼1.3 for Eu0.2Yb0.2Ca0.6Mg2Bi2 at 873 K. Density-functional theory (DFT) simulation indicates the alloying has no effect on the valence band, but does affect the conduction band. Such band engineering results in good p-type thermoelectric properties with high carrier mobility. Using transmission electron microscopy, various types of strains are observed and are believed to be due to atomic mass and size fluctuations. Point defects, strain, dislocations, and nanostructures jointly contribute to phonon scattering, confirmed by the semiclassical theoretical calculations based on a modified Debye–Callaway model of lattice thermal conductivity. This work indicates Bi-based (Ca,Yb,Eu)Mg2Bi2 is better than the Sb-based Zintl phases.

scholarly journals Theoretical Study on the Mechanism of Hydrogen Donation and Transfer for Hydrogen-Donor Solvents during Direct Coal Liquefaction

Catalysts ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 648 ◽  
Author(s):  
Haigang Hao ◽  
Tong Chang ◽  
Linxia Cui ◽  
Ruiqing Sun ◽  
Rui Gao
Keyword(s):  
Density Functional ◽  
Hydrogen Gas ◽  
Hydrogen Donor ◽  
Coal Liquefaction ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Donor Solvent ◽  
National Energy Security ◽  
Liquefaction Process ◽  
Direct Coal Liquefaction

As a country that is poor in petroleum yet rich in coal, it is significant for China to develop direct coal liquefaction (DCL) technology to relieve the pressure from petroleum shortages to guarantee national energy security. To improve the efficiency of the direct coal liquefaction process, scientists and researchers have made great contributions to studying and developing highly efficient hydrogen donor (H-donor) solvents. Nevertheless, the details of hydrogen donation and the transfer pathways of H-donor solvents are still unclear. The present work examined hydrogen donation and transfer pathways using a model H-donor solvent, tetralin, by density functional theory (DFT) calculation. The reaction condition and state of the solvent (gas or liquid) were considered, and the specific elementary reaction routes for hydrogen donation and transfer were calculated. In the DCL process, the dominant hydrogen donation mechanism was the concerted mechanism. The sequence of tetralin donating hydrogen atoms was α-H (C1–H) > δ-H (C4–H) > β-H (C2–H) > γ-H (C3–H). Compared to methyl, it was relatively hard for benzyl to obtain the first hydrogen atom from tetralin, while it was relatively easy to obtain the second and third hydrogen atoms from tetralin. Comparatively, it was easier for coal radicals to capture hydrogen atoms from the H-donor solvent than to obtain hydrogen atoms from hydrogen gas.

scholarly journals Electrocatalytic CO2 hydrogenation to C2 based products through C–C coupling over Cu(100) nanocube

2021 ◽  
Author(s):  
Shyama Charan Mandal ◽  
Biswarup Pathak
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Co2 Hydrogenation ◽  
Periodic Surfaces ◽  
Mechanistic Investigation ◽  
Hydrogenation Reactions

In this study, we have considered a Cu nanocube (Cu-NC) based catalyst exposed with (100) facets for CO2 hydrogenation reactions. All the feasible mechanistic pathways for the formations of C1 (HCOOH, CH3OH and CH4) and C2 (C2H4 and C2H5OH) based products have been explored using the density functional theoretical calculations and the most plausible pathways have been identified. The calculated results are compared with the previous reports on the periodic Cu(100) and Cu(111) surfaces, and also on the surface of Cu85 nanocluster and Cu(111) monolayer. The in-depth mechanistic investigation shows that Cu-NC can be very selective towards the C2 based products with a lower limiting potential (calculated) compared to the periodic surfaces. The underlying reasons for such findings have been explained and compared that with the periodic surfaces. We therefore, propose that the Cu-NC based catalysts can be more promising for C2 based products.

scholarly journals Efficient Synthesis, Spectral, Characterization, Antimicrobial and DFT Studies of Antimony(III) Dithiocarbamates

2021 ◽  
Vol 34 (1) ◽  
pp. 42-52
Author(s):  
S. Tamilvanan
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Mulliken Charge ◽  
Diffusion Method ◽  
Hydrogen Atoms ◽  
Gram Positive Bacteria ◽  
Antimicrobial Studies ◽  
Fungal Organisms ◽  
Ft Ir

The synthesis and characterization of novel antimony(III) dithiocarbamate complexes tris(N-furfuryl- N-propyldithiocarbamato-S,S′)antimony(III) (1) and tris(N-furfuryl-N-butyldithiocarbamato- S,S′)antimony(III) (2) have been characterized by elemental analysis, FT-IR, NMR (1H and 13C) spectra and antimicrobial studies. The characteristic thioureide (νC-N) bands occur at 1462 and 1475 cm-1 for complex 1 and 2, respectively. The theoretical calculations of the complexes have been carried out by density functional theory (DFT). The FMOs, MEP, Mulliken charge distribution and chemical activity parameters of the optimized structure have been calculated at the same level of theory. The MEP structure indicated that the positive and negative potential sites are around hydrogen atoms and electronegative atoms of the studied complexes, respectively. The Agar-well diffusion method were used to study the antimicrobial activity of the complexes against two Gram-positive bacteria (Klebsiella pneumoniae and Staphylococcus aureus), two Gram-negative bacteria (Escherichia coli and Vibrio cholera) and two fungal organisms (Candida albicans and Aspergillus niger).

Benchmarking Density Functionals, Basis Sets, and Solvent Models in Predicting Thermodynamic Hydricities of Organic Hydrides

2021 ◽  
Author(s):  
Christina Yeo ◽  
Minh Nguyen ◽  
Lee-Ping Wang
Keyword(s):  
Density Functional ◽  
Mean Squared Error ◽  
Theoretical Calculations ◽  
Computational Cost ◽  
Hydrogen Gas ◽  
Basis Set ◽  
Basis Sets ◽  
Density Functionals ◽  
Solvent Models ◽  
Solvent Model

Many renewable energy technologies, such as hydrogen gas synthesis and carbon dioxide reduction, rely on chemical reactions involving hydride anions. When selecting molecules to be used in such applications, an important quantity to consider is the thermodynamic hydricity, which is the free energy required for a species to donate a hydride anion. Theoretical calculations of thermodynamic hydricity depend on several parameters, mainly the density functional, basis set, and solvent model. In order to assess the effects of the above three parameters, we carry out hydricity calculations for a set of molecules with known experimental hydricity values, generate linear �fits, and compare the R-squared, root-mean-squared error, and Akaike Information Criterion across different combinations of density functionals, basis sets, and solvent models. Based on these results we are able to quantify the accuracy of theoretical predictions of hydricity and recommend the parameters with the best compromise between accuracy and computational cost.

scholarly journals Crystal structure of pantoprazole sodium sesquihydrate Form I, C16H14F2N3O4SNa(H2O)1.5

2020 ◽  
Vol 35 (1) ◽  
pp. 53-60
Author(s):  
Diana Gonzalez ◽  
Joseph T. Golab ◽  
James A. Kaduk ◽  
Amy M. Gindhart ◽  
Thomas N. Blanton
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Powder Diffraction ◽  
Density Functional ◽  
Water Molecules ◽  
Hydrogen Atoms ◽  
Powder Diffraction File ◽  
Trigonal Bipyramidal ◽  
Pyridine Nitrogen ◽  
Coordination Spheres

The crystal structure of pantoprazole sodium sesquihydrate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Pantoprazole sodium sesquihydrate crystallizes in space group Pbca (#61) with a = 33.4862(6), b = 17.29311(10), c = 13.55953(10) Å, V = 7852.06(14) Å3, and Z = 16. The crystal structure is characterized by layers parallel to the bc-plane. One layer contains the Na coordination spheres. The two independent sodium ions are trigonal bipyramidal and octahedral. The NaO3N2 and NaO4N2 coordination spheres share an edge to form pairs. The sodium bond valence sums are 1.17 and 1.15. The difluoromethyl groups are probably disordered. Two water molecules act as hydrogen bond donors to pyridine nitrogen atoms and sulfoxide oxygen atoms. The third water molecule participates in bifurcated hydrogen bonds, but one of its hydrogen atoms does not participate in hydrogen bonds. The powder pattern is included in the Powder Diffraction File™ as entry 00-065-1424.

scholarly journals Theoretical Investigation of the Quasi-ring C–H…π Interactions

2021 ◽  
Vol 18 (2) ◽  
pp. 119-128
Author(s):  
Sin Ang Lee ◽  
◽  
Zaidi Ab Ghani ◽  
Mohd Hafiz Yaakob ◽  
Mohamed Ismail Mohamed-Ibrahim ◽  
...  
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Basis Set ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Crystalline Materials ◽  
Π Interactions ◽  
Linear Chains ◽  
Moller Plesset ◽  
The Stability

The quasi-ring C–H…π interactions have been reported to be responsible for the stability of crystalline materials. The statistical analysis, together with electronic structure calculations in the framework of density functional theory and Moller-Plesset have also provided positive data on the aforementioned interactions. However, improvements can be had in the theoretical calculations, where the basis set convergence is not explored. This is crucial as the interactions are of weak type, reported to be around 4 – 5 kcal mol–1. In this investigation, the idea is to combine the geometry, potential energy surface, and bonding analysis to provide different insights into the interactions. Our results show that the original configurations of the crystals, even with the substitutions of linear chains, are more favorable than the rotated ones. Further calculations are needed to verify the involvements of the π orbitals of the N, C, Cl, S and the d-orbital of Cu, and the s-orbital of hydrogen atoms.

Theoretical and Experimental Evaluation of the Effect of Fluorinated Substituent on the Topological Landscape and Thermodynamic Stability of Zeolitic Imidazolate Framework Polymorphs

2018 ◽  
Author(s):  
Mihails Arhangelskis ◽  
Athanassis Katsenis ◽  
Novendra Novendra ◽  
Zamirbek Akimbekov ◽  
Dayaker Gandrath ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Mechanochemical Synthesis ◽  
Thermodynamic Stability ◽  
Experimental Evaluation ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Zeolitic Imidazolate Framework ◽  
Functional Theory ◽  
Calorimetric Measurements ◽  
And Calorimetry

By combining mechanochemical synthesis and calorimetry with theoretical calculations, we demonstrate that dispersion-corrected periodic density functional theory (DFT) can accurately survey the topological landscape and predict relative energies of polymorphs for a previously inaccessible fluorine-substituted zeolitic imidazolate framework (ZIF). Experimental screening confirmed two out of three theoretically anticipated polymorphs, and the calorimetric measurements provided an excellent match to theoretically calculated energetic difference between them.<br>

Magnetic Volume Effect of Hydrogen Diffusion in Palladium

2020 ◽  
Vol 310 ◽  
pp. 29-33
Author(s):  
Sarantuya Nasantogtokh ◽  
Xin Cui ◽  
Zhi Ping Wang
Keyword(s):  
Transition Metal ◽  
Density Of States ◽  
Density Functional ◽  
Hydrogen Diffusion ◽  
Magnetic Moments ◽  
Interstitial Site ◽  
Volume Effect ◽  
Face Centered Cubic ◽  
Hydrogen Atoms ◽  
Octahedral Interstitial Site

The electronic and magnetic properties of palladium hydrogen are investigated using first-principles spin-polarized density functional theory. By studying the magnetic moments and electronic structures of hydrogen atoms diffusing in face-centered cubic structure of transition metal Pd, we found that the results of magnetic moments are exactly the same in the two direct octahedral interstitial site-octahedral interstitial site diffusion paths-i.e. the magnetic moments are the largest in the octahedral interstitial site, and the magnetic moments are the lowest in saddle point positions. We also studied on the density of states of some special points, with the result that the density of states near the Fermi level is mainly contributed by 4d electrons of Pd and the change of magnetic moments with the cell volume in the unit cell of transition metal Pd with a hydrogen atom.

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