Halogen,hydrogen and electrostatic interactions in 2‐amino‐5‐chloro‐1,3‐benzoxazol‐3‐ium nitrate and 2‐amino‐5‐chloro‐1,3‐benzoxazol‐3‐ium perchlorate

In the title compounds, C₇H₆ClN₂O⁺·NO₃⁻ and C₇H₆ClN₂O⁺·ClO₄⁻, the ions are connected by N—H...O hydrogen bonds and halogen interactions. Additionally, in the first compound, co‐operative π–π stacking and halogen...π interactions are observed. The energies of the observed interactions range from a value typical for very weak interactions (1.80 kJ mol⁻¹) to one typical for mildly strong interactions (53.01 kJ mol⁻¹). The iminium cations exist in an equilibrium form intermediate between exo‐ and endocyclic. This study provides structural insights relevant to the biochemical activity of 2‐amino‐5‐chloro‐1,3‐benzoxazole compounds.     

Examination of the structures,energetics, and vibrational frequencies of small sulfur-containing prototypical dimers, (H2S)2 and H2O/H2S

The optimized geometries, vibrational frequencies, and dissociation energies from MP2 and CCSD(T) computations with large correlation consistent basis sets are reported for (H₂S)₂ and H₂O/H₂S. Anharmonic vibrational frequencies have also been computed with second-order vibrational perturbation theory (VPT2). As such, the fundamental frequencies, overtones, and combination bands reported in this study should also provide a useful road map for future spectroscopic studies of the simple but important heterogeneous H₂O/H₂S dimer in which the hydrogen bond donor and acceptor can interchange, leading to two unique minima with very similar energies. Near the CCSD(T) complete basis set limit, the HOH⋯SH₂ configuration (H₂O donor) lies only 0.2 kcal mol⁻¹ below the HSH⋯OH₂ structure (H₂S donor). When the zero-point vibrational energy is included, however, the latter configuration becomes slightly lower in energy than the former by <0.1 kcal mol⁻¹. © 2018 Wiley Periodicals, Inc.     

Comparison of Proton Acceptor and Proton Donor Properties of H2O and H2O2 in Organic Crystals of Drug-like Compounds: Peroxosolvates vs. Crystallohydrates

Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (H₂O₂) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (H₂O) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by H₂O₂ as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by H₂O. In the case of H₂O₂ as a proton acceptor in H-bonds, the ratio appeared reversed. The neutral O∙∙∙H-O/O∙∙∙H-N bonds formed by the lone electron pair of the oxygen atom of water were the strongest H-bonds in the considered crystals. In the paper, it was found out that the low-frequency Raman spectra of isomorphous crystalline hydrate and peroxosolvate of N-(5-Nitro-2-furfurylidene)-1-aminohydantoin are similar. As for the isostructural hydrate and peroxosolvate of the salt of protonated 2-amino-nicotinic acid and maleic acid monoanion, the Raman spectra are different.     

Determination of long-range intermolecular interaction energies using RPA/moment function methods. Application to H2O,H2O2 and H2O/H2O2 mixtures

The fully expanded expression for the Boltzmann-averaged pairwise intermolecular interaction energy of two molecules of arbitrary symmetry in the long-range (interaction < kT) limit has recently been determined explicitly as a series in r⁻ⁿ (r is the intermolecular separation) for n < 11. The resultant expression contains only multipolar products (point moment functions: PMFs) and energy terms which are characteristic of the ground state and excitation properties of the isolated molecules. These quantities are determined for H₂O and H₂O₂ using the single particle-hole RPA method, and the interaction energy contributions determined by direct state summation. Static electric dipole polarizabilities are determined as a by-product of the procedure, and are shown to agree closely with finite field results using a comparable basis. For the chiral H₂O₂/H₂O₂ system, the r⁻⁶ and r⁻⁹ discrimination energies are also calculated, suggesting that the r⁻⁹ contributions could well exceed the r⁻⁶ discriminatory terms for separations less than 20 au.     

The structure of decomposing [C7H7O]+ ions: Benzyl versus tropylium ion structures

The unimolecular dissociation reactions for [C₇H₇O]⁺ ions generated by fragmentation of a series of precursor molecules have been investigated. The metastable kinetic energy values and branching ratios associated with decarbonylation and expulsion of a molecule of formaldehyde (CH₂O) from the [C₇H₇O]⁺ ions are interpreted as the hydroxybenzyl and hydroxytropylium [C₇H₇O]⁺ not interconverting to a common structure on the microsecond time-scale. In addition, similar measurements on protonated benzaldehyde, methylaryloxy and phenyl methylene ether [C₇H₇O]⁺ ions are interpreted as the dominant fraction of these decomposing ions having unique structures on the microsecond time-scale. These results are supported by experimental heats of formation calculated from ionization/appearance energy measurements. The experimental heats of formation are determined as: hydroxybenzyl ions, 735 kJ mol^?1; hydroxytropylium ions, 656 kJ mol^?1; phenyl methylene ether ions, 640 kJ mol^?1; methylaryloxy ions 803 kJ mol^?1. The combination of the results reported in this paper with previously reported experimental data for stable [C₇H₇O]⁺ ions (see Ref. 1, C. J. Cassady, B. S. Freiser and D. H. Russell, Org. Mass Spectrom.) is interpreted as evidence that the relative population of benzyl versus tropylium [C₇H₇O]⁺ ion structures from a given precursor molecule is determined by isomerization of the parent ion and not by structural equilibration of the [C₇H₇O]⁺ ion.     

Hydroxidmonohydrate des Kaliums und Rubidiums; Verbindungen,deren Atomanordnungen die Schreibweise K(H2O)OH bzw. Rb(H2O)OH nahelegen

Hydroxide Monohydrates of Potassium and Rubidium; Compounds with Atomic Arrangements which Suggest the Formula K(H₂O)OH and Rb(H₂O)OH Single crystals for x-ray structure investigations of the monohydrates of potassium and rubidium hydroxides were obtained by recrystallization of microcrystalline sampels in supercritical ammonia as solvent. The structure determination on both structurally closely related compounds was successful up to the localization of the hydrogen positions. Besides the monohydrates were characterized by IR spectra and thermochemical data. The atomic arrangement of the compounds is discussed in comparison to the one of substances as PbFCl, γ-AlOOH etc. In addition to the chemical bonds in the stated compounds both monohydrates show one-dimensional infinite hydrogen bridges between the H atoms of the water molecules and the hydroxide ions; furthermore weak H bonds connect the OH^? ions. Because the hydroxide ions are involved in two bridge-bindung systems water molecules are the nearest neigh-bours of the cations.     

Is selective hydrogenation of molecular oxygen to H2O2 affected by strong metal–support interactions on Pd/TiO2 catalysts? A case study using commercially available TiO2

In this study, titania-supported Pd catalysts were prepared and their performance evaluated upon H₂O₂ direct synthesis. Typically, the materials contained different ratios of anatase and rutile phases, which gave rise to different surface properties of the supports, e.g., surface area, number of Lewis acidic and basic sites as well as different compositions of the phases, i.e. the amount of anatase phase and crystallite size. Two materials, Pd-A98 and Pd-A05 samples, respectively, apparently hint the existence of the so-called SMSI (strong metal–support interaction) phenomenon giving rise to 1080 and 683 mol_H2O2·mol_Pd⁻¹·h⁻¹ of H₂O₂ productivity and 22 and 14% of H₂O₂ selectivity, respectively. However, the best material, Pd-A82, gave rise to 949 mol_H2O2·mol_Pd⁻¹·h⁻¹ of H₂O₂ productivity and 26% of H₂O₂ selectivity.     

Activation energy of thermal decomposition of fully dehydrated NdC2O4Cl·3H2O to NdOCl

An activation energyE _a=195 kJ mol^?1 has been determined for the thermal decomposition of NdC₂O₄Cl to NdOCl with simultaneous expulsion of CO and CO₂. As compared with the value (127 kJ mol^?1) predicted by the Kahwa-Mulokozi empirical expression (i) for Ln₂(C₂O₄)₃ (Ln=light lanthanide), the presence of Cl^? in the coordination polyhedron appreciably raises the activation energy, which is consistent with a corresponding increase in the covalent strength of the Ln-oxalate bond. The same conclusion regarding the strength of this bond is drawn from a study of the infrared spectrum. Mechanistically, the breaking of the Ln-oxalate bond is suggested to occur in the kinetic ratedetermining step.     

Neutron diffraction analysis at 15 K and ab initio molecular orbital calculations for α-cyanoacetohydrazide: A crystal structure with a high energy conformer

The crystal structure of α-cyanoacetohydrazide, C₃H₅N₃O, is refined using single-crystal neutron diffraction data at 15 K. Nuclear equilibrium geometries of the isolated molecules are calculated using GAUSSIAN-82 for the eight possible conformers having C_s symmetry. The conformation observed in the crystal has the eighth highest calculated energy, 36.6 kJ mol⁻¹ above the lowest energy conformer, and the largest calculated dipole moment, 8.6 D, with a HF/6-31G* basis. In the crystal the molecule is distorted from the ideal C_s symmetry. These distortions add another 20.3 kJ mol⁻¹ in energy, calculated with HF/6-31G*. All the hydrogens, including the CH, are involved in intermolecular hydrogen-bonding which is unusual in that it is formed entirely by three-center bonds. These bonds form a network which includes dimer and chain configurations.     

The distonic ions HO+CHCH2C˙H2 and CH3C(O+H)CH2C˙H2

The distonic ions HO⁺?CHCH₂C^˙H₂ (1) and CH₃C(?O⁺H)CH₂C^˙H₂ (2) were directly generated, their decompositions characterized and their appearance energies determined by photoionization. Heats of formation derived from the appearance energies were 757 kJ mol^?1 for 1 and 692 kJ mol^?1 for 2. Deuterium labeling demonstrates that both ions decompose at low energies in the same ways as their isomers with the same skeletal structures, consistent with proposals that 1 and 2 are intermediates in the decompositions of those systems. Surprisingly, the values of the translational energy releases accompanying the formation of CH₃CO⁺ and C₂H₅CO⁺ from 2 appear to be inversely proportional to the available excess energy. The 1,2-H-shift RC(?O⁺H)CH₂C˙H₂ → RC(?O₊H)C˙HCH₃ is compared to the corresponding, non-occurring 1,2-H-shift in alkyl free radicals.     

Stationary points on the energy hypersurface of the reaction O3 + H•→ [•O3H]* ⇆ O2 + •OH and thermodynamic functions of •O3H at G3MP2B3, CCSD(T)-CBS (W1U) and MR-ACPF-CBS levels of theory

The relative enthalpies, ΔH^o (0) and ΔH^o (298.15), of stationary points (four minimum and three transition structures) on the ^•O₃H potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)–CBS (W1U) procedures from which we earlier found mean absolute deviations (MAD) of 3.9 kJ mol⁻¹ and 2.3 kJ mol⁻¹, respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For CCSD(T)-CBS (W1U) the well depth from O₃ + H^• to trans-^•O₃H, ΔH^o_well(298.15) = −339.1 kJ mol⁻¹, as well as the reaction enthalpy of the overall reaction O₃ + H^•→O₂ + ^•OH, Δ_rH^o(298.15) = −333.7 kJ mol⁻¹, and the barrier of bond dissociation of trans-^•O₃H → O₂ + ^•OH, ΔH^o(298.15) = 22.3 kJ mol⁻¹, affirm the stable short-lived intermediate ^•O₃H. In addition, for radicals cis-^•O₃H and trans-^•O₃H, the thermodynamic functions heat capacity C^o_p(T), entropy S^o (T), and thermal energy content H^o(T) − H^o(0) are tabulated in the range of 100 − 3000 K. The much debated calculated standard enthalpy of the formation of the trans-^•O₃H resulted to be Δ_fH^o(298.15) = 31.1 kJ mol ⁻¹ and 32.9 kJ mol ⁻¹, at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied to consider possible multiconfiguration effects and yield Δ_fH^o(298.15) = 21.2 kJ mol ⁻¹. The discrepancy between calculated values and the experimental value of −4.2 ± 21 kJ mol⁻¹ is still unresolved. Note added in proof: Yu-Ran Luo and J. Alistair Kerr, based on the discussion in reference 12, recently presented an experimental value of Δ_fH^o(298.15) = 29.7 ± 8.4 kJ mol⁻¹ in the 85th edition of the CRC Handbook of Chemistry and Physics (in progress).     

Synthesis, Characterization and Thermochemistry of 2MgO：B2O3：1.5H2O

Introduction　　 2MgO·B2 O3(Mg2 B2 O5)and 2MgO·B2 O3·H2 Omightbepreparedaswhiskermaterials .12MgO·B2 O3·H2 OnamedszaibelyiteisamagnesiumboratemineralwithastructuralformulaofMg2 [B2 O4 (OH) 2 ].2 Itisdifficulttosynthesizethiscompoundinthelaboratory .Recently ,weobtainedasimilarcompound 2MgO·B2 O3·1 5H2 Owhenwetriedtopreparewhiskerof 2MgO·B2 O3·H2 Obythephasetransformationof 2MgO·2B2 O3·MgCl2 ·14H2 OinH3BO3solutionunderhydrothermalcondition .Itishope fultopreparewh…     

Zur Koordination des Aluminiums in den Calciumaluminathydraten 2 CaO · Al2O3 · 8 H2O und CaO · Al2O3 · 10 H2O

On the Coordination of Al in the Calcium Aluminate Hydrates 2 CaO · Al₂O₃ · 8 H₂O and CaO · Al₂O₃ · 10 H₂O By investigations with high-resolution ²⁷Al-NMR in solids it is shown that in the compound 2 CaO · Al₂O₃ · 8 H₂O the Al merely exist in octahedral coordination. According to this and considering its structural relationship with 4 CaO · Al₂O₃ · 19 H₂O the dicalcium aluminate hydrate is proposed to be formulated as [Ca₂Al(OH)₆][Al(OH)₃ (H₂O)₃]OH. Likewise for the compound CaO · Al₂O₃ · 10 H₂O the octahedral coordination of the Al is proved by ²⁷Al-NMR. This result corresponds with literature according to which a constitution as cyclohexaaluminate Ca₃[Al₆(OH)₂₄] · 18 H₂O is proposed.     

Two scandium–biuret complexes: [Sc(C2H5N3O2)(H2O)5]Cl3·H2O and [Sc(C2H5N3O2)4](NO3)3

The scandium(III) cations in the structures of pentaaqua(biuret‐κ²O,O′)scandium(III) trichloride monohydrate, [Sc(C₂H₅N₃O₂)(H₂O)₅]Cl₃·H₂O, (I), and tetrakis(biuret‐κ²O,O′)scandium(III) trinitrate, [Sc(C₂H₅N₃O₂)₄](NO₃)₃, (II), are found to adopt very different coordinations with the same biuret ligand. The roles of hydrogen bonding and the counter‐ion in the establishment of the structures are described. In (I), the Sc³⁺ cation adopts a fairly regular pentagonal bipyramidal coordination geometry arising from one O,O′‐bidentate biuret molecule and five water molecules. A dense network of N—H...Cl, O—H...O and O—H...Cl hydrogen bonds help to establish the packing, resulting in dimeric associations of two cations and two water molecules. In (II), the Sc³⁺ cation (site symmetry 2) adopts a slightly squashed square‐antiprismatic geometry arising from four O,O′‐bidentate biuret molecules. A network of N—H...O hydrogen bonds help to establish the packing, which features [010] chains of cations. One of the nitrate ions is disordered about an inversion centre. Both structures form three‐dimensional hydrogen‐bond networks.     

CoC2O4·2H2O在空气中的热分解动力学研究

纳米Co3O4具有尖晶石结构,Co3 占据八面体位,具有较高的晶体场稳定化能,在空气中低于800℃时十分稳定,是优良的催化材料[1]。Co3O4还可以作为高比能锂离子电池负极材料具有非常好的电化学活性,充放电容量高达960m A h·g-1。纳米Co3O4在紫外、可见及近红外区域都有良好的吸收效果,因此,在隐身技术、保温节能技术等领域具有潜在的应用前景。所以,Co3O4超细粉体的制备和应用研究具有十分重要的意义。我们合成了草酸盐先驱物制备纳米Co3O4用作隐身材料,因此对先驱物的热分解过程研究是十分必要的。热分析方法在了解先驱物热分解反应的物理…     

Equilibrium and Kinetic Studies on Ligand Substitution Reactions of Trans-[COIII(en)2(Me)H2O]2+: A Model for Coenzyme B12

Ligand substitution of trans-[Co^III(en)₂(Me)H₂O]²⁺ was studied for pyrazole, 1,2,4-triazole and N-acetylimidazole as entering nucleophiles. These displace the coordinated H₂O molecule trans to the methyl group to form trans-[Co(en)₂(Me)azole]. Stability constants at 18°C for the substitution of H₂O by pyrazole, 1,2,4-triazole and N-acetylimidazole are 0.7 ± 0.1, 13.8 ± 1.4 and 1.7 ± 0.2 M^?1, respectively. Second order rate constants at the same temperature for the reaction of trans-[Co^III(en)₂(Me)H₂O]²⁺ with pyrazole, 1,2,4-triazole and N-acetylimidazole are 161 ± 12, 212 ± 11 and 12.9 ± 1.6 M^?1 s^?1, respectively. Activation parameters (ΔH^≠, ΔS^≠) are 67 ± 6 kJ mol^?1, + 27 ± 19 J K^?1 mol^?1; 59 ± 2 kJ mol^?1, + 1 ± 6 J K^?1 mol^?1 and 72 ± 4 kJ mol^?1, + 23 ± 14 J K^?1 mol^?1 for reactions with pyrazole, 1,2,4-triazole and N-acetylimidazole, respectively. Substitution of coordinated H₂O by azoles follows an I_d mechanism.     

Syntheses and crystal structures of [Na(H2O)](C17H13O6SO3)* 2H2O and [NKH2O)6]C17H13O6SO3)2*H2O

Two hydrates of sodium 5,7‐dihydroxy‐6,4′‐dimethoxyisoflavone‐3′‐sulfonate ([Na(H₂O)J(C₁₇H₁₃O₆SO₃)*2H₂O,] 1) and nickel 5,7‐dihydroxy‐6,4′‐dimethoxyisoflavone‐3′‐sulfonate ([Ni(H₂O)₆](C₁₇H₁₃O₆SO₃)₂*4H₂O, 2) were synthesized and characterized by IR, 'H NMR and X‐ray diffraction analyses. The hydrate 1 crystallizes in the mono‐clinic system, space group P2(1) with a=0.8201(9) nm, b=0.8030(8) nm, c= 1.5361(16) nm, β=102.052(12)°, V =0.9893(18) nm³, D,= 1.579 g/cm³, Z=2, μ=0.252 nm^?1, F(000)=488, R=0.0353, wR=0.0873. The hydrate 2 belongs to triclinic system, space group P‐1 with a=0.7411(3) nm, b=0.8333(3) nm, c=1.7448(7) nm, α= 86.361(6)°, β=86.389(5)°, γ= 88.999(3)°, V=1.0731(7) nm³, D,=1.587 g/cm³, Z=1, μ=0.649 m^?1, F(000)= 534. In the structure of 1, the sodium cation is coordinated by six oxygen atom and two adjacent ones are bridged by three oxygen atoms to form an octahedron chain. The C? H…?… hydrogen bonds exist between two isoflavone molecules in the structure of 2. Meanwhile, hydrogen bonds in two compounds, link themselves to assemble two three‐dimensional network structures, respectively.     

Raman spectroscopy study of species responsible for the fast proton conductivity in H2Sb4O11.3H2O

The Raman spectroscopy study of crystallized antimonic acid trihydrate powders in the 20–4000 cm⁻¹ confirme the explicit formula : (H₃O⁺)_2−x[Sb₄O_11−xOH_x]^−(2−x).(3+x−2)H₂O. Furthermore it emphasizes the presence of hydrogen bonds between either the SbOSb bridge and H₃O⁺ or the protonated Sb(OH)Sb bridge and H₂O.     

Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The R_N and/or A_M models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol^–1 (R_1.575, stage I); 101 kJ mol^–1 (Ain1.725 stage II); 185 kJ mol^–1 (A _2.9, stage III) and in argon: 66 kJ mol^–1 (A _1.25, stage I); 87 kJ mol^–1 (A _1.825, stage II); 133 kJ mol^–1 (A _2.525, stage III).     

Metal–Organic Framework (MOF)-Derived Electron-Transfer Enhanced Homogeneous PdO-Rich Co3O4 as a Highly Efficient Bifunctional Catalyst for Sodium Borohydride Hydrolysis and 4-Nitrophenol Reduction

Developing a bifunctional catalyst with low cost and high catalytic performance in NaBH₄ hydrolysis for H₂ generation and selective reduction of nitroaromatics will make a significant impact in the field of sustainable energy and water purification. Herein, a low-loading homogeneously dispersed Pd oxide-rich Co₃O₄ polyhedral catalyst (PdO-Co₃O₄) with concave structure is reported by using a metal–organic framework (MOF)-templated synthesis method. The results show that the PdO-Co₃O₄ catalyst has an exceptional turnover frequency (3325.6 mol_H2 min⁻¹ mol_Pd⁻¹), low activation energy (43.2 kJ mol⁻¹), and reasonable reusability in catalytic H₂ generation from NaBH₄ hydrolysis. Moreover, the optimized catalyst also shows excellent catalytic performance in the NaBH₄ selective reduction of 4-nitrophenol to 4-aminiphenol with a high first-order reaction rate of approximately 1.31 min⁻¹. These excellent catalytic properties are mainly ascribed to the porous concave structure, monodispersed Pd oxide, as well as the unique synergy between PdO and Co₃O₄ species, which result in a large specific surface area, high conductivity, and fast solute transport and gas emissions.