Theoretical investigation of the structure and properties of H2B=NH2...Mn+, HB≡NH...Mn+, and Borazine...Mn+ complexes (M = Alkaline and Earth Alkaline Metals)

The nature of H₂B=NH₂...M ⁿ⁺, HB=NH...M ⁿ⁺, and Borazine...M ⁿ⁺ interactions were studied with ab-initio calculations. The interaction energies were calculated at B3LYP/6-31G(d, p) level. The calculations suggest that the size and charge of cation are two influential factors that affect the nature of interaction. The theory of atoms in molecules (AIM) and natural bond orbital (NBO) analysis of complexes indicate that the variation of densities and the extent of charge shifts upon complexation correlate well with the obtained interaction energies.     

Kinetic study of oxidative coupling of methane over Mn and/or W promoted Na_2SO_4/SiO_2 catalysts

A comprehensive kinetic model for oxidative coupling of methane(OCM)over Mn and/or W promoted Na2SO4/SiO2 catalysts was developed based on a micro-catalytic reactor data.The methane conversion and ethylene,ethane,carbon monoxide and carbon dioxide selectivities were obtained in a wide operating condition range of 750 - 825-C,CH4/O2=2.5 - 10 and contact time=267 - 472 kg s m-3.Reaction networks of six models with different rate equation types were compared together.The kinetic rate parameters of each reaction network were estimated using linear regression or genetic algorithm optimization method(GA).A reaction network suggested by Stansch et al.for OCM was found to be the best one and was further used in this work.The suggested model could predict the experimental results of OCM reaction within a deviation range of ± 20%.     

Substitute Effect on the Structure,Stability of Valence Isomers and Aromaticity of 1‐H‐Boratabenzene

Density functional theory (B3LYP) calculations were performed on the Me and F substituted valence isomeric forms of 1‐H‐boratabenzene. The calculations revealed that the planar benzene analog is the lowest energy isomer. Its aromaticity is analyzed in the light of the nucleus‐independent chemical shift (NICS) and shows that aromaticity increases in F substituted, but decreases in Me substituted. These calculations indicate substitution of BH with BMe and BF doesn't cause significant variation in bond length.     

Effect of citric acid and starch as emulsifier on phase formation and crystallite size of lanthanum oxide nanoparticles

Lanthanum oxide nanoparticles were synthesized via thermal decomposition method of the lanthanum nitrate in the presence of citric acid or starch as emulsifier. The effects of emulsifier and calcination temperature were investigated on the phase transformation and particle size distribution of the products. La₂O₃ nanoparticles were synthesized by drying lanthanum precursor and emulsifier solution, followed by calcination process at 600 and 900°C, respectively. Products were characterized by Fourier Transform Infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), thermal analysis (TG/DTA) and nitrogen adsorption method (porous characteristics). The morphology of the samples analyzed using scanning electron microscopy (SEM). Average crystallite size of the products was calculated by XRD data and average particle size was measured from the TEM micrographs. Lanthanum dioxycarbonate in different forms of the tetragonal and monoclinic is crystallized in the presence of citric acid and starch during the calcination at 600°C, respectively. The hexagonal structure, however, is detected as the only crystalline phase formed by calcination at 900°C.     

Dynamic stereochemistry of erigeroside by measurement of 1H-1H and 13C-1H coupling constants

Erigeroside was extracted from Satureja khuzistanica Jamzad (Marzeh Khuzistani in Persian, family of lamiaceae), and (1)H, (13)C, (13)C{(1)H}, (1)H-(1)H COSY, HMQC and J-HMBC were obtained to identify this compound and determine a complete set of J-coupling constants ((1)J(C-H), (2)J(C-H), (3)J(C-H) and (3)J(H-H)) values within the exocyclic hydroxymethyl group (CH(2)OH) and anomeric center. In parallel, density functional theory (DFT) using B3LYP functional and split-valance 6-311++G** basis set has been used to optimized the structures and conformers of erigeroside. In all calculations solvent effects were considered using a polarized continuum (overlapping spheres) model (PCM). The dependencies of (1)J, (2)J and (3)J involving (1)H and (13)C on the C(5')-C(6') (omega), C(6')-O(6') (theta) and C(1')-O(1') (phi) torsion angles in erigeroside were computed using DFT method. Complete hyper surfaces for (1)J(C1',H1'), (2)J(C5',H6'R), (2)J(C5',H6'S), (2)J(C6',H5'), (3)J(C4',H6'R), (3)J(C4',H6'S) and (2)J(H6'R-H5'S) as well as (3)J(H5',H6'R) were obtained and used to derive Karplus equations to correlate these couplings to omega, theta and phi. These calculated J-couplings are in agreement with experimental values. These results confirm the reliability of DFT calculated coupling constants in aqueous solution.     

DFT and TD-DFT study of benzene and borazines containing chromophores for DSSC materials

In this investigation, we have designed a series of benzene and borazines containing chromophores for employing in dye-sensitized solar cells (DSSCs). The optimized structures and photo-physical properties of these molecules have been explored by using the density functional theory method (B3LYP/6-311++G(d,p)). These dyes consist of electron-donor (benzene, borazine, fluorinated borazine) and -acceptor/anchoring (tricyanovinyl), connected by the π-conjugated linker as an electron spacer. The Natural Bond Orbital (NBO) analysis has also been employed for studying the origin of charge transfer. The time-dependent density functional theory (TD-DFT) method has also been used to calculate the electronic absorption spectra of these molecules. The maximum absorption wavelengths assign to HOMO → LUMO transition. The electronic coupling constant, electron injection and light harvesting efficiency have been computed by first principle researches. This revealed that the studied molecules would be efficient photosensitizers.     

Theoretical Study of the Solvent Effect on the Electronic and Vibrational Properties of [CpFe(CO)<Subscript>2</Subscript>(NCS)] and [CpFe(CO)<Subscript>2</Subscript>(SCN)] Linkage Isomers

The present study illustrates the stability of [CpFe(CO)₂(NCS)] and [CpFe(CO)₂(SCN)] linkage isomers by the use of MPW1PW91 quantum method in the gas and solution phases. Our results reveal that the [CpFe(CO)₂(NCS)] isomer is more stable than the [CpFe(CO)₂(SCN)] isomer. Based on the polarizable continuum model, the effect of the solvent polarity on the stability, structural parameters, frontier orbital energies, and vibrational modes of carbonyl ligands (ν_CO) of these linkage complexes is explored. The molecular orbital analysis suggests that the major contributions to HOMO and LUMO arise from the ambidentate ligand and Fe in two isomers, respectively. In addition, the bonding interaction between the CpFe(CO)₂ fragment and the ambidentate ligand is studied by means of the energy decomposition analysis. The back-bonding effect in Fe–CO bonds is revealed in the calculation of the quadrupole polarization of the carbon atom by the QTAIM analysis. The character of Fe–N and Fe–S bonds in these complexes is analyzed by the natural bond orbital analysis.     

Theoretical Study of the Interactions Between Borthiin and Fluorinated Borthiins with Difluorine

The nature of borthiin and fluorinated borthiin interactions with difluorine was studied with ab initio calculations. The interaction energies were calculated at the B3LYP/6-311+G(d,p) level. Vibrational and AIM analyses of the complexes indicate that the variation of densities correlates well with the obtained interaction energies. Also, the nucleus independent chemical shift (NICS) values have been used for studying aromaticity in species. These values suggest that aromaticity increases in complexes.     

Conformational study of a strained tolanophane by dynamic 1H NMR spectroscopy and computational methods

The existence of a short C–H ⋯ π (alkyl–alkyne) interaction in the structure of a strained and relatively rigid tolanophane is expected to hinder the rotation about the C–C sp³ single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl₃, THF-d₈, and acetone-d₆) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined at coalescence (210 K) with acetone-d₆ which is in good agreement with calculation result (54 kJ/mol). Correspondence: Hossein Reza Darabi, Chemistry and Chemical Engineering Research Center of Iran, Pajoohesh Blvd., km 17, Karaj Hwy, 14968-13151 Tehran, Iran.     

Substituent Effect on the Thermodynamics and Kinetics of Carbyne Complex [(η5-C5H5)(CO)(COMe)Re≡CC6H4X] Isomerization to Carbene Complex [(η5-C5H5)(CO)2Re=C(Me)(para-C6H4X]: A Theoretical Study

Russian Journal of Physical Chemistry A - This study investigates the effect of different substituents on the isomerization reaction of the [(η5‑C5H5)(CO)(Me)Re≡CC6H5] carbyne...