Journal of Molecular Structure-theochem最新文献

The interaction between CdS and acetylacetone as a complexing agent is examined. We have performed conformational searches, optimizations and frequency calculations in the MP2/LANL2DZ level of theory. The importance of acetylacetone lies in its ability to tautomerize and form stable compounds through the accessibility of the physical position of its oxygens.

The first hyperpolarizabilities β and ultraviolet spectra of two-dimensional charge transfer (2DCT) donor/acceptor-functionalized trigonal dehydrobenzoannulenes (compounds 2–7) have been calculated by using ab initio quantum chemistry methods. It is found that these multiple substituted chromophores possess large β values, where both diagonal and off-diagonal terms play important roles in β. This is different from the typical one-dimensional charge transfer (1DCT) compounds, where β is dominated by the diagonal terms. It is worth noting that a good nonlinearity-transparency trade-off is achieved for compounds 2–7 which exhibit larger β values coupled with enhanced transparency in the visible region. Moreover, the contributions of dipolar components to β are larger than that of octupolar components for compounds 2–7.

The performance of a variety of density functional theories (DFT) used for calculating N–O bond dissociation enthalpies (BDEs) of quinoxaline-1,4-dioxide derivatives is examined. It was observed that mPW1PW91, B3LYP, B1B95, and BMK functionalities significantly outperformed other popular density functional theory methods, including B3PW91, B1LYP, and B3P86. In particular, the mPW1PW91 method was recommended because of its accuracy. Subsequently, first, second, total, and mean N–O BDEs for a new synthetic veterinary medicine, Quinocetone, were determined. The predictions obtained via the mPW1PW91 were 240.4, 251.0, 508.4, and 254.2 kJ mol⁻¹, respectively.

By the aid of density-functional theory and all-electron numerical basis set, we have found 40 stable isomers of ${\text{Fe}}_n{\text{O}}_m^{+}$ (n + m = 5) clusters through optimization calculations and frequency analysis from 161 initial structures. The binding energies, the energy gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital and the magnetic moments of all the stable isomers are reported. The relationships between the molecular properties and structures are examined.

Theoretical studies on the spectral and DNA-photocleavage properties of Co(III) and Ru(II) polypyridyl complexes [M(phen)₂(pyip)]ⁿ⁺ (M = Co(III) and Ru(II), n = 3 and 2, respectively) have been carried out, using DFT, HF and CIS methods. The electronic absorption spectra of the two complexes were calculated and simulated using TDDFT and CPCM model. The calculated results show that both the geometric structure and spectra of the Co(III) complex are greatly affected by the solvent effect, whereas those of the Ru(II) complex are affected only slightly by the solvent effect. The calculated and simulated spectra of these complexes in solution are in satisfying agreement with experimental ones, and the characters of the interested spectral bands are deeply discussed. In addition, the photo-induced oxidation–reduction mechanisms on the DNA-photocleavage by Co(Ш) and Ru(II) polypyridyl complexes are also preliminarily explained in theory.

Since double bonded systems constituted by higher main group elements are necessarily substituted by bulky substituents, in order to protect these structures kinetically, van der Waals interactions are dominant on the resulting bonding energies. This aspect, studied in detail with different density functional methods for a variety of selected disilenes, is compared with the results of MP2 calculations. Throughout a triple-ζ basis set was used, in order to allow flexible bonding. The bonding energies in the disilenes were characterized by dissociation into singlet silylenes. For the parent disilene the equilibrium was studied in addition with CCSD calculations utilizing Dunning type basis sets. The corrections for dispersion energies on the functionals BP86, PBE, and B3LYP were at times evaluated according to the Grimme approach, and the results compared with the refit double-hybrid functional BP97-D and MP2. They are sizable for the bulky systems. The only known case of reversible silylene–disilene in equilibrium is studied too. This silylene is known in a cis or trans conformation, with a stronger steric stronger congestion in the cis geometry. The dispersion corrections on stability favor to more extent the more encumbered geometries. Overall the calculations indicate that the traditional density functionals, like B3LYP or BP86 are not capable to describe properly the bulky molecular structures.

Quantum chemistry calculations have been performed by using Gaussian03 program to compute optimized geometry, harmonic vibrational frequency. Atomic charges at HF/6-31G(d, p), B3LYP/6-31G(d, p) and B3LYP/6-311++G(d, p) levels for 1-(2,6-Dichloro-4-nitrophenyl)-5-amino-4-cyanopyrazole (C₁₀H₁₀Cl₂N₅O₂) in the ground state are also calculated. The research shows that the presence of strong hydrogen bonding in the title compound. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR spectra. A detailed interpretation of the infrared spectra of the title compound is reported. The theoretical spectrograms for FT-IR spectra of the title compound have been constructed. In addition, the ¹³C NMR and other molecular properties are further investigated.

1,1-Diamino-2,2-dinitroethene (FOX-7) was theoretically synthesized in both aqueous and gaseous environment in this study, based on experience of experimental methods, from 2-methylimidazole via oxidation followed by nitration and aminolysis. Reaction routes closely related to experimental processes were successfully constructed, and the corresponding kinetic rate constants and energy barriers were estimated for each elementary reaction. Furthermore, other reaction conditions that are distinct from those reported in the literature (including the use of a solvated oxidative reaction system, the replacement of nitrating agent HNO₃ by N₂O₅, and the adoption of cupric oxide or ferrous oxide catalysts for aminolysis) were employed in the corresponding reaction systems. The modeling results suggest that water is a good medium for the oxidation reaction, N₂O₅ is the better agent for nitration, and ferrous oxide is a suitable catalyst for aminolysis in hydrated systems. In contrast with the computed activation energies of the experimental routes, the comparable data estimates throughout the reaction stages were considered to imply more feasible pathways for FOX-7 synthesis.

Theoretical study of several benzyl nitrites have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G∗∗ basis set. Geometries obtained from DFT calculations were used to perform NBO analysis. It is noted that weakness in the O₃–N₂ sigma bond is due to $n_{\text{O}1}\to {\sigma }_{\text{O}3''–''\text{N}2}^{\ast }$ delocalisation and is responsible for the longer O₃–N₂ bond lengths in the selected benzyl nitrites. It is also noted that decreased occupancy of the localized ${\sigma }_{\text{O}3''–''\text{N}2}$ orbital in the idealized Lewis structure, or increased occupancy of ${\sigma }_{\text{O}3''–''\text{N}2}^{\ast }$ of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital (NHO) of ${\sigma }_{\text{O}3''–''\text{N}2}$ bond orbital. In addition, the charge transfer energy decreases with the increasing of the Hammett constants of substituent groups.

Density functional calculations have been utilized to understand the interactions of sulfur hexafluoride (SF₆) with α-cyclodextrin (α-CD) host. An encapsulation of SF₆ (guest) within the host cavity and its binding to primary as well as secondary hydroxyl rims of α-CD exhibiting different hydrogen bonding patterns have been analyzed. The present calculations have shown that interactions between the guest and protons within the host cavity yield the minimum energy complex wherein guest penetrates from secondary hydroxyl end of the host. Calculated vibrational spectra reveal frequency downshift of S–F stretching in the guest molecule on complexation. Frequency shift in opposite direction has been noticed for O–H vibrations of secondary hydroxyls of the host those facilitate relatively strong hydrogen bonded interactions. These inferences have been supported by mapping difference molecular electron density on the bond critical points in molecular electron density topography. The electronic structure and vibrational spectra derived from the density functional calculations based on the B3LYP and the X3LYP functional are similar. Use of X3LYP functional however, predicts shortening of O6H⋯O6′ as well as CH⋯F hydrogen bonds and thus points to the strengthened host–guest interactions and in turn binding energies of SF₆ within these complexes employing the X3LYP functional turn out to be nearly ∼35–40% higher compared to those obtained within the framework of B3LYP theory.