Chemical bonding and properties in [Ni(N-heterocylic carbene)(NO)(R)] (R = H, Me, HC=CH2, and C≡CH) complexes: Theoretical insights

A series of N-heterocyclic carbene nickel complexes of the type [Ni(N-heterocylic carbene)(NO)(R)] (R = H, Me, HC=CH₂, and C≡CH) are examined to study the influence of a substituent on the molecular structure and bonding of these complexes. Geometrical and AIM analyses of the interaction between Ni and the carbene fragment reveal that for the metal-carbene bond donation is more important than back-donation. The NICS values suggest that aromaticity in the heterocyclic ring is less than in the free heterocycle.     

Modeling of biliverdin reduction process: regio-specificity and H-bonding

Octa ethyl biliverdin (OEBV) has been employed as a model for natural biliverdin and its geometry has been optimized by using semiempirical (AM1, PM3), DFT, and hybrid ONIOM methods. Geometries and energetics of formation of octa ethyl bilirubin (OEBR) formed by reduction from OEBV via three carbon sites β, γ, and δ have been obtained. It has been shown that γ-OEBR has two configurational isomers (named γ₁ and γ₂), which can convert to each other by internal 1,5-hydrogen shift. The results show that, within the accuracy level of semiempirical methods, all three isomers namely, β, γ₁, and δ-OEBR are of similar stability whereas, at higher level of theory, γ₁-OEBR is less stable than others. Moreover, γ₂-isomer with one more of its pyrrole rings being aromatic can achieve a higher symmetry, and is the most stable among others by at least 5–6 kcal mol⁻¹ based on various methods employed. It is interesting to note that the ridge-tile conformation, which has been confirmed for natural bilirubin was not observed for calculated geometries of γ₁- and γ₂-isomers. A conformational analysis show that an energy barrier of 25 kcal mol⁻¹ must be surmounted for γ₂ to obtain the ridge-tile geometry.

OEBV was synthesized and purified from octa ethyl porphyrin iron (III) chloride, and was reduced to OEBR by sodium borohydride (NaBH₄). Chemical reduction of OEBV with NaBH₄ was followed in CDCl₃ and CD₃OD solutions and the product was characterized by ¹H NMR and UV–Vis spectroscopy. The results show that γ₂-isomer as the major product, forms along with γ₁ via an equilibrium tautomerization reaction.     

Optimal capacitor placement to minimizing cost and power loss in Tehran metro power distribution system using ETAP (A case study)

Most loads in the power distribution system of Tehran Metro (Subway) are inductive and lead to poor power factor (PF) especially in Lighting and Power Substation. One of the methods of PF correction is adding or producing the capacitive components within the circuit to eliminate the effect of inductive loads. Optimal capacitor placement (OCP), with the objects of power system voltage profile improvement, PF correction, loss reduction, and line reactive power decrease are of particular importance in power system control and planning. These objects depend on how the capacitive components are installation and to achieve them, since the capacitor placement is nonlinear problem and has some equally and inequality constraint. This article investigates OCP in the actual power distribution grid of Tehran Metro (Line 2) in the presence of nonlinear loads. The placement problem is solved using Genetic Algorithms as implemented in the Electrical Transient Analyser Program software. Results (capacity release, total generation, loading, demand, power losses and number of capacitor banks, costs and annual benefits) are obtained and analysed. This study and simulation shows that by OCP can calculate reduce annual losses and release capacity of equipment in power distribution grid of Tehran Metro such as cables and transformers from reactive power and that will maximize profits. © 2016 Wiley Periodicals, Inc. Complexity 21: 483–493, 2016     

Borepine: A Density Functional Approach toward Structural Features and Properties

The structure and properties of borepine and substituted borepines have been studied theoretically at the B3LYP/6-311++G(d,p) level. The calculations include the frontier orbitals, vibrational analysis, optical properties, electronic spectrum analysis, aromaticity and thermodynamic. The effects of the substituent groups on the structure, electronic properties, ionization potential (IP), electron affinity (EA), and reorganization energy has been studied. Aromaticity of molecules has been explored based on NICS values and delocalization index. The NICS values indicated increasing of aromaticity in electron withdrawing substituents.     

Synthesis of CaCO3 nanoparticles via citrate method and sequential preparation of CaO and Ca(OH)2 nanoparticles

Calcium carbonate nanoparticles were synthesized via so‐called sol–gel citrate method using calcium nitrate as precursor in presence of different concentration of citric acid, selected to be 0.0, 0.5, 1.25 and 2.5 times of the concentration of the precursor, on calcining at 600 °C for 5 h. Stable phase of the calcite is formed in presence of citric acid. The roles of organic additive concentration, calcination temperature and sonication on the particle size of the products were investigated. Calcium oxide nanoparticles were prepared by facial calcination of the resulted product at 900 °C for 5 h. Calcium hydroxide nanoparticles, however, were synthesized on sonication of the product for 20 min in water at room temperature. Samples were characterized by XRD and FT‐IR studies. Crystallite size of samples was calculated by XRD data and was measured by TEM analysis. The specific surface are (SSA) of samples was calculated by the XRD data and compared by the measured BET. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantum mechanical study of energetics and mechanisms of cis–trans isomerization of some four-membered heterocycles

Ab initio quantum mechanical calculations using density functional (B3LYP) method and 6-311G** basis set have been performed on two cis and trans conformers of 2,4-diphenyl thietane dioxide (DPTD), 2,4-diphenyl thietane (DPT), 2,4-diphenyl azetidine (DPA) and 2,4-diphenyl oxetane (DPO). The calculated stability energy for cis–trans isomerization in gas phase and in different solvents such as benzene, DMSO, water and methanol indicated that the cis conformer is more stable than trans in all above-mentioned compounds about 11–2 kcal mol^?1. In the next step, a transition states for cis–trans inter-conversion for all four-membered heterocycles (DPTD, DPT, DPA and DPO) were proposed in methanol as solvent. Thermodynamic functions such as standard enthalpies of isomerization (?Hº_iso), standard entropy of isomerization (?Sº_iso) and standard Gibbs free energy of isomerization (?Gº_iso) for all studied compounds were also evaluated. The calculation showed that the conversion of trans to cis isomer is exothermic and spontaneous. In all calculations, solvent effects were considered using a polarized continuum model.     

HYDROGEN ADSORPTION AND STORAGE ON PALLADIUM-FUNCTIONALIZED GRAPHYNE AND ITS BORON NITRIDE ANALOGUE

Journal of Structural Chemistry - This study investigates adsorption of a hydrogen molecule on palladium-functionalized graphyne and its boron nitride analogue using the mPW1PW91 functional. The...     

Molecular interaction of H2 and H2O with borthiin: a theoretical study

A density functional theory at the B3LYP/6-311G(d,p) level was applied to investigate the impact of hydrogen and water molecules on borthiin. The calculated binding energies of complexes were corrected for the basis set superposition error. The changes in structural parameters and in chemical hardness values were calculated for borthiin interacting with H₂ and H₂O. The strength of the weak interaction between borthiin and the H₂ and H₂O molecules was analyzed using the topological properties according to the ??Atoms in Molecules?? theory by Bader. The factors influencing the strength of the interaction between the borthiin and the H₂ and H₂O molecules were considered in detail using the NBO analysis. The vibrational frequencies and the intensities of the B-H stretching bands were calculated. The nucleus independent chemical shift (NICS) method was used to study the aromaticity of borthiin and the complexes.     

A quantum chemical study of Cr(CO)3(B3N3H6 ? n F n ) (n = 1–3) complexes

The electronic structure and properties of Cr(CO)₃(B₃N₃H_{6 ? n} F _n ) (n = 1?C3) complexes have been explored using hybrid density functional B3LYP theory. Calculations indicate B-fluorinated isomers are more stable, and less polarizable, than N-fluorinated isomers. The aromatic natures of the borazine rings have been analyzed by nucleus independent chemical shift (NICS). The atoms in molecules (AIM) analysis indicates that Cr-C and Cr-N bonds distance is well correlated with the electron density of critical point (??_cp) in all species.