Crystals, Volume 6, Issue 2 (February 2016) – 6 articles

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

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

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

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

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

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