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Crystals, Volume 6, Issue 2 (February 2016)

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Research

Open AccessArticle In situ Synchrotron X-ray Thermodiffraction of Boranes
Crystals 2016, 6(2), 16; doi:10.3390/cryst6020016
Received: 19 December 2015 / Revised: 15 January 2016 / Accepted: 21 January 2016 / Published: 25 January 2016
Cited by 3 | PDF Full-text (1707 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Boranes of low molecular weight are crystalline materials that have been much investigated over the past decade in the field of chemical hydrogen storage. In the present work, six of them have been selected to be studied by in situ synchrotron X-ray thermodiffraction.
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Boranes of low molecular weight are crystalline materials that have been much investigated over the past decade in the field of chemical hydrogen storage. In the present work, six of them have been selected to be studied by in situ synchrotron X-ray thermodiffraction. The selected boranes are ammonia borane NH3BH3 (AB), hydrazine borane N2H4BH3 (HB), hydrazine bisborane N2H4(BH3)2 (HBB), lithium LiN2H3BH3 (LiHB) and sodium NaN2H3BH3 (NaHB) hydrazinidoboranes, and sodium triborane NaB3H8 (STB). They are first investigated separately over a wide range of temperature (80–300 K), and subsequently compared. Differences in crystal structures, the existence of phase transition, evolutions of unit cell parameters and volumes, and variation of coefficients of thermal expansion can be observed. With respect to AB, HB and HBB, the differences are mainly explained in terms of molecule size, conformation and motion (degree of freedom) of the chemical groups (NH3, N2H4, BH3). With respect to LiHB, NaHB and STB, the differences are explained by a stabilization effect favored by the alkali cations via M···H interactions with four to five borane anions. The main results are presented and discussed herein. Full article
(This article belongs to the Special Issue Boron-Based (Nano-)Materials: Fundamentals and Applications)
Open AccessArticle Synthesis, Crystal Structural Investigations, and DFT Calculations of Novel Thiosemicarbazones
Crystals 2016, 6(2), 17; doi:10.3390/cryst6020017
Received: 8 January 2016 / Revised: 26 January 2016 / Accepted: 28 January 2016 / Published: 2 February 2016
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Abstract
The crystal and molecular structures of three new thiosemicarbazones, 2-[1-(2-hydroxy-5-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide monohydrate (1), 2-[1-(2-hydroxy-5-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide (2) and 2-[1-(2-hydroxy-4-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide acetonitrile solvate (3), are reported and confirmed by single crystal X-ray diffraction, NMR and UV-vis
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The crystal and molecular structures of three new thiosemicarbazones, 2-[1-(2-hydroxy-5-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide monohydrate (1), 2-[1-(2-hydroxy-5-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide (2) and 2-[1-(2-hydroxy-4-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide acetonitrile solvate (3), are reported and confirmed by single crystal X-ray diffraction, NMR and UV-vis spectroscopic data. Compound (1), C11H15N3O2S·H2O, crystallizes in the monoclinic with space group P21/c, with cell parameters a = 8.2304(3) Å, b = 16.2787(6) Å, c = 9.9708(4) Å, and β = 103.355(4)°. Compound (2), C12H17N3O2S, crystallizes in the C2/c space group with cell parameters a = 23.3083(6) Å, b = 8.2956(2) Å, c = 13.5312(3) Å, β = 91.077(2)°. Compound (3), C11H15N3O2S·C2H3N, crystallizes in the triclinic P-1 space group with cell constants a = 8.9384(7) Å, b = 9.5167(8) Å, c = 10.0574(8) Å, α = 110.773(7)°, β = 92.413(6)°, and γ = 90.654(7)°. DFT B3LYP/6-31(G) geometry optimized molecular orbital calculations were also performed and frontier molecular orbitals of each compound are displayed. The correlations between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound have been proposed. Additionally, similar correlations observed among three closely related compounds, (4), 2-[1-(2-hydroxy-4-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide, (5), 2-[1-(2-hydroxy-6-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide acetonitrile monosolvate and (6), 2-[1-(2-hydroxy-6-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide, examining structural differences from the substitution of the methoxy group from the phenyl ring (4, 5, or 6 position) and the substitution of the terminal amine (methyl or ethyl) to their frontier molecular orbital surfaces and from their Density Functional Theory (DFT) molecular orbital energies provide further support for the suggested assignments of the title compounds. Full article
(This article belongs to the Section Biomolecular Crystals)
Open AccessArticle Crystal-Structure Analysis with Moments of the Density-of-States: Application to Intermetallic Topologically Close-Packed Phases
Crystals 2016, 6(2), 18; doi:10.3390/cryst6020018
Received: 5 November 2015 / Revised: 22 January 2016 / Accepted: 25 January 2016 / Published: 2 February 2016
Cited by 3 | PDF Full-text (1608 KB) | HTML Full-text | XML Full-text
Abstract
The moments of the electronic density-of-states provide a robust and transparent means for the characterization of crystal structures. Using d-valent canonical tight-binding, we compute the moments of the crystal structures of topologically close-packed (TCP) phases as obtained from density-functional theory (DFT) calculations. We
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The moments of the electronic density-of-states provide a robust and transparent means for the characterization of crystal structures. Using d-valent canonical tight-binding, we compute the moments of the crystal structures of topologically close-packed (TCP) phases as obtained from density-functional theory (DFT) calculations. We apply the moments to establish a measure for the difference between two crystal structures and to characterize volume changes and internal relaxations. The second moment provides access to volume variations of the unit cell and of the atomic coordination polyhedra. Higher moments reveal changes in the longer-ranged coordination shells due to internal relaxations. Normalization of the higher moments leads to constant (A15,C15) or very similar (χ, C14, C36, μ, and σ) higher moments of the DFT-relaxed TCP phases across the 4d and 5d transition-metal series. The identification and analysis of internal relaxations is demonstrated for atomic-size differences in the V-Ta system and for different magnetic orderings in the C14-Fe 2 Nb Laves phase. Full article
(This article belongs to the Special Issue Intermetallics)
Open AccessArticle H2XP:OH2 Complexes: Hydrogen vs. Pnicogen Bonds
Crystals 2016, 6(2), 19; doi:10.3390/cryst6020019
Received: 6 January 2016 / Revised: 25 January 2016 / Accepted: 28 January 2016 / Published: 2 February 2016
Cited by 4 | PDF Full-text (1502 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A search of the Cambridge Structural Database (CSD) was carried out for phosphine-water and arsine-water complexes in which water is either the proton donor in hydrogen-bonded complexes, or the electron-pair donor in pnicogen-bonded complexes. The range of experimental P-O distances in the phosphine
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A search of the Cambridge Structural Database (CSD) was carried out for phosphine-water and arsine-water complexes in which water is either the proton donor in hydrogen-bonded complexes, or the electron-pair donor in pnicogen-bonded complexes. The range of experimental P-O distances in the phosphine complexes is consistent with the results of ab initio MP2/aug’-cc-pVTZ calculations carried out on complexes H2XP:OH2, for X = NC, F, Cl, CN, OH, CCH, H, and CH3. Only hydrogen-bonded complexes are found on the H2(CH3)P:HOH and H3P:HOH potential surfaces, while only pnicogen-bonded complexes exist on H2(NC)P:OH2, H2FP:OH2, H2(CN)P:OH2, and H2(OH)P:OH2 surfaces. Both hydrogen-bonded and pnicogen-bonded complexes are found on the H2ClP:OH2 and H2(CCH)P:OH2 surfaces, with the pnicogen-bonded complexes more stable than the corresponding hydrogen-bonded complexes. The more electronegative substituents prefer to form pnicogen-bonded complexes, while the more electropositive substituents form hydrogen-bonded complexes. The H2XP:OH2 complexes are characterized in terms of their structures, binding energies, charge-transfer energies, and spin-spin coupling constants 2hJ(O-P), 1hJ(H-P), and 1J(O-H) across hydrogen bonds, and 1pJ(P-O) across pnicogen bonds. Full article
(This article belongs to the Special Issue Analysis of Hydrogen Bonds in Crystals) Printed Edition available
Open AccessFeature PaperArticle 5-Azido-4-dimethylamino-1-methyl-1,2,4-triazolium Hexafluoridophosphate and Derivatives
Crystals 2016, 6(2), 20; doi:10.3390/cryst6020020
Received: 14 January 2016 / Revised: 1 February 2016 / Accepted: 2 February 2016 / Published: 5 February 2016
Cited by 1 | PDF Full-text (9682 KB) | HTML Full-text | XML Full-text
Abstract
5-Azido-4-(dimethylamino)-1-methyl-1,2,4-triazolium hexafluoridophosphate was synthesized from the corresponding 5-bromo compound with NaN3. Reaction with bicyclo[2.2.1]hept-2-ene yielded a tricyclic aziridine, addition of an N-heterocyclic carbene resulted in a triazatrimethine cyanine, and reduction with triphenylphosphane gave the 5-amino derivative. The crystal structures of
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5-Azido-4-(dimethylamino)-1-methyl-1,2,4-triazolium hexafluoridophosphate was synthesized from the corresponding 5-bromo compound with NaN3. Reaction with bicyclo[2.2.1]hept-2-ene yielded a tricyclic aziridine, addition of an N-heterocyclic carbene resulted in a triazatrimethine cyanine, and reduction with triphenylphosphane gave the 5-amino derivative. The crystal structures of three nitrogen-rich salts were determined. Thermoanalysis of the cationic azide and triazene showed exothermal decomposition. The triazene exhibited negative solvatochromism in polar solvents involving the dipolarity π* and hydrogen-bond donor acidity α of the solvent. Full article
(This article belongs to the Special Issue Nitrogen-Rich Salts)
Open AccessArticle Preparation, Crystal and Properties of Nitrogen-Rich Energetic Salt of Bis(semicarbazide) 5,5′-Bitetrazole-1,1′-diolate
Crystals 2016, 6(2), 21; doi:10.3390/cryst6020021
Received: 26 December 2015 / Accepted: 3 February 2016 / Published: 6 February 2016
Cited by 4 | PDF Full-text (2297 KB) | HTML Full-text | XML Full-text
Abstract
A novel energetic salt of Bis(semicarbazide) 5,5′-bitetrazole-1,1′-diolate [2(SCZ)·BTO] was synthesized by using semicarbazide hydrochloride and 1H,1’H-5,5’-bitetrazole-1,1’-diol (BTO) as raw materials, and its structure was characterized by elemental analysis, Fourier Transform infrared spectroscopy (FT-IR) spectroscopy, 13C NMR spectrum and
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A novel energetic salt of Bis(semicarbazide) 5,5′-bitetrazole-1,1′-diolate [2(SCZ)·BTO] was synthesized by using semicarbazide hydrochloride and 1H,1’H-5,5’-bitetrazole-1,1’-diol (BTO) as raw materials, and its structure was characterized by elemental analysis, Fourier Transform infrared spectroscopy (FT-IR) spectroscopy, 13C NMR spectrum and mass spectrum. The single crystal of the title salt was obtained and its structure was determined by an X-ray single-crystal diffractometer. Results show that 2(SCZ)·BTO belongs to the monoclinic space group P21/c with a density of 1.685 g·cm−3. The thermal decomposition behavior was investigated by differential scanning calorimetry (DSC) and thermogravimetry-derivative thermogravimetry (TG-DTG) analyses, and non-isothermal kinetic parameters were also calculated. The results indicated that it has a good thermal stability with a decomposition temperature above 200 °C. The apparent activation energies were 231.2 kJ·mol−1 (Kissinger's method) and 228.1 kJ·mol−1 (Ozawa-Doyle's method), respectively, and the critical temperature of thermal explosion is 240.6 °C. The enthalpy of formation for the salt was calculated as 158.1 kJ·mol−1. The detonation pressure (P) and detonation velocities (D) of the salt were determined by using the Kamlet-Jacobs equation. The results indicated that the title salt has potential applications in the field of energetic materials. Full article
(This article belongs to the Special Issue Nitrogen-Rich Salts)
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