Theoretical prediction of the electronic and thermodynamic properties of YN‐ZrN solid solutions

In this study, the results of structural parameters, electronic structure, and thermodynamic properties of the Zr_xY_1–xN solid solutions are presented. The effect of zirconium composition on lattice constant, and bulk modulus shows nonlinear dependence on concentration. Deviations of the lattice constant from Vegard's law and deviations of the bulk modulus from linear concentration dependence were found. Our findings indicate that the Zr_xY_1–xN solid solutions are metallic for x = 0.25, 0.5, 0.75. The calculated excess mixing enthalpy is positive over the entire zirconium composition range. The positive mixing enthalpies for Zr_xY_1–xN alloys indicate the existence of miscibility gaps and spinodal decompositions. The effect of temperature on the volume, bulk modulus, Debye temperature, and the heat capacity for Zr_xY_1–xN alloys were analyzed using the quasi‐harmonic Debye model. Results show that the heat capacity is slightly sensitive to composition as temperature increases. © 2015 Wiley Periodicals, Inc.     

A combined computational and experimental approach for investigating a hydrogen‐bonded supermolecular compound comprising benzimidazole and malonic acid

A hydrogen‐bonded tetramer supramolecular motif of 2:2 benzimidazole (BIZ) and malonic acid (MLA) has been synthesized and characterized by elemental analysis, infrared (IR), and X‐ray single crystal diffraction. Thermal stability analyses demonstrate that this supramolecular adduct is a new material and it is not the ordinary superposition of the original monomers. Density function theory (DFT) calculations for the models of dimers, trimers, and tetramer comprising BIZ and MLA have been carried out at B3LYP/6‐31G* and PBE1PBE/6‐31G* levels of theory, respectively. By comparing the calculated results with the experiments (single crystal structure, IR spectra, and thermal analysis) and based on the statistic thermodymnamic calculations, it is concluded that the dimers cannot exist at room temperature and the tetramer can simulate the title supramolecular complex better than the two trimers. Further studies on the model of tetramer indicate that the hydrogen bond of N···H? O is stronger than that of O···H? N. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Relative Thermodynamic Stabilities of Isomeric Dimethyl Acetals Derived from 2-Acetyltetrahydrofuran. An Experimental and Computational Study

In the presence of an acid catalyst, the dimethyl acetal of 2-acetyltetrahydrofuran (1) is converted into a mixture of three isomeric acetals composed of the reactant and two diastereomers of 2-methoxy-2-(1-methoxyethyl)tetrahydrofuran (2). The relative thermodynamic stabilities of these acetals have now been determined by chemical equilibration. The least stable isomer is 1, in the liquid phase 4–6 kJ mol^–1 less stable than the two diastereomers. The geometry-optimized structures and relative energies of the title compounds were also studied by theoretical calculations (ab initio and DFT). Comparison of the theoretically determined relative stabilities of the diastereomers with the corresponding experimental data suggests the more volatile (and more stable) diastereomer to exist as a racemic mixture of the (R,S) and (S,R) configurations.     

Synthesis,Characterization and Theoretical Studies on a Thiocarbamide Derivative Containing Schiff Base Group

A thiocarbamide derivative containing Schiff base groups,1,5-bis[4-(dimethylamino)benzylidene]thiocarbonohydrazide,has been synthesized and characterized by elemental analysis,IR,1H NMR,UV and X-ray single-crystal diffraction.Density function theory(DFT) calculations at the B3LYP/6-31G* and PBE0/6-31G* levels for optimized geometries and electronic transition spectra have been performed.Comparative studies show that both B3LYP/6-31G* and PBE0/6-31G* methods can well reproduce the molecular structure,and the latter is more reliable than the former to simulate electronic spectra.NPA calculational results at the B3LYP/6-31G* level indicate the title compound to be a potential multidentate ligand to the metallic ions.Based on the vibrational analysis,thermodynamic properties at different temperatures have been obtained.     

Stabilization in neutral bicyclic sulfoxide compounds

Density Functional Theory (DFT) calculations at the B3LYP/6‐31+G* level have been performed on 5‐thiabicyclo[2.1.1]hex‐2‐ene S‐oxide derivatives. The geometrical and electronic properties of the compounds have been analyzed in order to explain the favored stability of the exo configuration. Isodesmic reactions at the Gaussian‐G2 theory yielded the exo conformer as the most stable one. Moreover, the NMR chemical shift parameters (GIAO method) together with the Atoms in Molecules theory reveal an stabilization of the S atom with the double bond for the exo configuration, in agreement with the experimental results. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 322–327, 2000     

Calculation of thermodynamic and transport properties of a typical arc furnace plasma

Using a previously developed computer program, thermodynamic and transport properties of a typical arc furnace plasma are calculated in order to single out those species and / or reactions which exert a dominating influence on the properties of such complex mixtures. The results indicate that dissociation of molecular species in the arc furnace atmosphere has a strong effect on the specific heat and on the thermal conductivity of the mixture. The electrical conductivity is strongly affected by metallic vapors from the molten metal pool and the slag cover.     

Electronic energy structure of Al<Subscript>x</Subscript>Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>C wide-gap semiconductor crystals

The electronic structure of silicon carbide solid solutions with aluminum has been studied within the limits of a single approximation. The local coherent potential method in terms of multiple scattering theory was used. The electronic spectrum was analyzed in comparison with the experimental X-ray spectra of silicon, aluminum, and carbon. The nature of the observed features of the electronic spectrum is interpreted, and Al-Si covalent binding in solid solutions is found. Formation of vacant states with energies of 1 Ry and decreased forbidden gap in the XANES spectrum at higher aluminum contents in crystal are discussed.     

Structural,magnetic, and vibrational properties of stoichiometric clusters of CrN

We performed density‐functional‐theoretic calculations to investigate the structural, magnetic and vibrational properties of the stoichiometric clusters (CrN)_n ( ). We show that the building block of the ground‐state structures of these clusters is a square CrNCrN unit; the only exception with n > 2 occurs for (CrN)₃, but this cluster has an isomer not very far in energy from the ground state consisting of a pair of CrNCrN squares sharing a CrN bond. In the smaller CrN, (CrN)₂, and (CrN)₃ clusters the magnetic moments of the N atoms are non‐negligible and antiparallel to those of the Cr atoms, but for the larger species (CrN)₄, (CrN)₅, (CrN)₆, and (CrN)₉ the cluster magnetic moments are almost entirely due to the Cr atoms. Lack of imaginary vibrational frequencies in the predicted ground‐state structures of (CrN)_n ( ) confirms that they are mechanically stable equilibrium states. © 2015 Wiley Periodicals, Inc.     

Structures and Properties of 1,2,3-Triazoles and 1,2,4-Triazoles

1 INTRODUCTION In the energetic material field, extensive attention was paid to insensitive compounds possessing not only high energetic density but also good stability. Previous studies[1] have shown that some small mo- lecular compounds such as azoles are good candi- dates for excellent explosives. For example, explo- sives containing triazole rings have the advantages of less molecular weight, high nitrogen content and density, good thermal stability, low impact sensiti- vity and large …     

Crystal Engineering of Supramolecular 1,4-Benzene Bisamides by Side-Chain Modification – Towards Tuneable Anisotropic Morphologies and Surfaces

Benzene bisamides are promising building blocks for supramolecular nano-objects. Their functionality depends on morphology and surface properties. However, a direct link between surface properties and molecular structure itself is missing for this material class. Here, we investigate this interplay for two series of 1,4-benzene bisamides with symmetric and asymmetric peripheral substitution. We elucidated the crystal structures, determined the nano-object morphologies and derived the wetting behaviour of the preferentially exposed surfaces. The crystal structures were solved by combining single-crystal and powder X-ray diffraction, solid-state NMR spectroscopy and computational modelling. Bulky side groups, here t-butyl groups, serve as a structure-directing motif into a packing pattern, which favours the formation of thin platelets. The use of slim peripheral groups on both sides, in our case linear perfluorinated, alkyl chains, self-assemble the benzene bisamides into a second packing pattern which leads to ribbon-like nano-objects. For both packing types, the preferentially exposed surfaces consist of the ends of the peripheral groups. Asymmetric substitution with bulky and slim groups leads to an ordered alternating arrangement of the groups exposed to the surface. This allows the hydrophobicity of the surfaces to be gradually altered. We thus identified two leitmotifs for molecular packings of benzene bisamides providing the missing link between the molecular structure, the anisotropic morphologies and adjustable surface properties of the supramolecular nano-objects.     

The synthesis,molecular, crystal,and electronic structures of [ReBr2(O)(OCH3)(PPh3)2]

[ReBr₂(O)(OCH₃)(PPh₃)₂] has been obtained in the reaction of [ReBr₃O(PPh₃)₂] or [ReBr₂(η²-N₂COPh-N′,O)(PPh₃)₂] with an excess of methanol. [ReBr₂O(OMe)(PPh₃)₂] crystallizes in the triclinic space group P-1. The complex was characterized by infrared, UV-Vis, and ¹H NMR spectra. The electronic structure of the obtained compound has been calculated using the DFT/TD–DFT method.     

Interactions of the “piano‐stool” [ruthenium(II) (η6‐arene)(en)CL]+ complexes with water and nucleobases; ab initio and DFT study

Piano stool ruthenium complexes of the composition [Ru(II)(η⁶‐arene)(en)Cl]^+/2+ (en = ethylenediamine) represent an emerging class of cisplatin‐analogue anticancer drug candidates. In this study, we use computational quantum chemistry to characterize the structure, stability and reactivity of these compounds. All these structures were optimized at DFT(B3LYP)/6‐31G(d) level and their single point properties were determined by the MP2/6‐31++G(2df,2pd) method. Thermodynamic parameters and rate constants were determined for the aquation process, as a replacement of the initial chloro ligand by water and subsequent exchange reaction of aqua ligand by nucleobases. The computations were carried out at several levels of DFT and ab initio theories (B3LYP, MP2 and CCSD) utilizing a range of bases sets (from 6‐31G(d) to aug‐cc‐pVQZ). Excellent agreement with experimental results for aquation process was obtained at the CCSD level and reasonable match was achieved also with the B3LYP/6‐31++G(2df,2pd) method. This level was used also for nucleobase‐water exchange reaction where a smaller rate constant for guanine exchange was found in comparison with adenine. Although adenine follows a simple replacement mechanism, guanine complex passes by a two‐step mechanism. At first, Ru‐O6(G) adduct is formed, which is transformed through a chelate TS2 to the Ru‐N7(G) final complex. In case of guanine, the exchange reaction is more favorable thermodynamically (releasing in total by about 8 kcal/mol) but according to our results, the rate constant for guanine substitution is slightly smaller than the analogous constant in adenine case when reaction course from local minimum is considered. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

Free-energy calculations of the host–guest association in grafted supramolecular assemblies

Herein, we investigate the impact of grafting macrocyclic hosts with hydrophobic cavities onto a gold surface on the association with a guest molecule of particular importance to applications for molecular machines. We establish that the increase of the grafted alkyl chain length and number of anchor points strengthens the binding of the guest with the β-cyclodextrin host. This is the opposite effect with the p-sulfonatocalix[4]arene host for which the grafting considerably reduces the strength of the host–guest association. The structural and thermodynamic characterizations, carried out with free energy simulations, are combined to rationalize the differences in the association process in both heterogeneous and homogeneous conditions.