Journal of Molecular Structure-theochem最新文献

Density function theory (DFT) has been applied to investigate the interactions between NO and N₂O with Cu⁺ species in a beta zeolite (BEA) at sites T1 and T9. The geometries for Cu-BEA represented as 10T cluster, and complexes of NO and N₂O adsorptions on them in η¹-O and η¹-N modes have been completely optimized. The calculated results showed that NOx could be adsorbed on Cu⁺ species in two modes, and N–O bond distances of NOx increase after adsorption. The adsorption energies of NO and N₂O molecules in η¹-N mode on Cu-BEA are larger than in η¹-O mode, and the interactions between N₂O or NO and Cu-BEA at site T9 are stronger than at T1 site.

Density functional theory (B3LYP) calculation is used to determine the gas-phase proton affinities of four series of nano-size diamines (1–2.3 nm) including –(CH₂)_n–C₆₀–(CH₂)_n–, –(C₆H₄)_n–, –(CHCH)_n–, and –(CH₂)_n– spacers, where the maximum value of n is 5, 5, 9 and 15, respectively. The results showed that, in the case of diamines with two former spacers the first proton affinity, PA₁, decreases by increasing the value of n, while in the case of two latter diamines it increases by increasing the value of n. However, the second proton affinity, PA₂, and proton overallaffinity, PA_ov, of all above molecules, as expected, increases with increasing the value of n. Among all above compounds the greatest amounts of the PA₁ and PA₂ were calculated for H₂NCH₂–C₆₀–CH₂NH₂ and H₂N–(CH₂)₁₅–NH₂ molecules, respectively. It seems that the C₆₀ molecule has an increasing effect on PA₁ of diamines, while a saturated long aliphatic chain which separates well the positively charged nitrogen atoms has an increasing effect on PA₂ of diamines. The above results has led us to design new nano-size superbases with –N(CH₃)₂ or –NC{N(CH₃)₂}₂ basic groups on fullerene molecule. The amounts of PA₁, PA₂ and PA_ov, for one of these superbases are 1126.3, 786.6 and 1912.9 kJ mol⁻¹, respectively, indicating that it is one of the strongest superbases known so far.

The enthalpies of formation of brominated benzenes and phenols were predicted using Gaussian-4 (G4), G3X, and G3XMP2 model chemistries and a few popular density functional methods, coupled with homodesmic reactions (HR1), (HR2) in which C₆H₆, C₆H₅Br, and C₆H₅OH are used as reference compounds. The results from G4, G3X, and G3XMP2 agree closely within 2 kJ/mol for all brominated benzenes and phenols; while the results from density functional methods are systematically higher than the G4 ones. The predicted enthalpies of formation for 2- and 4-bromophenols are in close agreement with the recent experimental measurements. Three reactions (R1), (R2), (R3) were also used to derive ${\Delta }_{\text{f}}{H}_{298\text{K}}^{°}$(g, C₆H₅Br) = 98.7 ± 1.0 kJ/mol by using CH₄, CH₃Br, CH₂Br₂, CH₂CHBr, and C₆H₆ as reference compounds at G4 and G3X levels. The value is significantly lower than the only experimental value of 105.4 kJ/mol given by Cox and Pilcher in 1970, and a re-determination is called.

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.

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.

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.

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.