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Abstract: The syn- and anti-conformers of 2-tellurophenecarboaldehyde are studied in the gas phase. A transition state is also modelled for the syn-anti isomerisation. Computations are done using different methods namely HF, DFT/B3LYP, MP2 and CCSD(T). The basis set used for all atoms is 6-311++G(d,p) except that LanL2DZ ECP is used for tellurium atom only. The optimised molecular structures and related structural parameters of these conformers are reported. The energy differences between the syn- and anti-conformers, associated rotational barriers and thermodynamic parameters are derived from the computations. The infrared frequencies of these conformers are also reported with appropriate assignments. This study is extended to include solvent effect and the conformers are fully optimised (DFT/B3LYP) using the integral equation formalism in the Polarisable Continuum model. In the gas phase, the theoretical rate constant for the unimolecular conversion, anti conformer to transition state, is reported for the first time; DFT/B3LYP (4.82×1030 s−1) and MP2 (7.81×1030 s−1). It is found that the structures are not much affected by the solvents but energy difference increases and rotational barrier decreases. The results indicate that there is a close agreement with the predictions from the different theoretical methods. The results obtained are critically analysed and compared with the furan, thiophene and selenophene analogues. A major factor affecting conformational preference and the mole fraction is the charge on the chalcogen heteroatom in the ring. An interesting outcome of this work is that in both the gas phase and solutions, the syn conformer is more stable and exists almost exclusively. [Copyright &y& Elsevier]

Abstract: Quantum mechanical methods have been employed to investigate the structural and spectroscopic properties of the novel trisilylsilylcyanide and trigermylgermylcyanide isolated molecules, in C3v symmetry, in the gas phase. The levels of theory used are DFT and MP2, the functional employed for the DFT method is B3LYP and the basis set used for all atoms is 6-311G(d,p). En route, the structures of these compounds have been analysed using the natural bond orbital approach. The latter confirms the presence of all single bonds and the only triple bond, namely, the Cn both of these molecules. Substituting silicon and germanium for carbon in the parent molecule, trimethylmethylcyanide, leave the bond length Cinvariant. Both the ab initio methods used perform satisfactorily when the predicted parameters from the two methods are compared. All the normal modes of vibrations were assigned to one of the 11 types of motion namely X–C stretch, X–X stretch, C, X–H stretch, X–X–C bend, X–X–X bend, X–C–X–H bend, XH3 rock, XH3 def and XH3 twist (X=Si or Ge). An interesting outcome of this work is that the HOMO–LUMO energy gap decreases from trimethylmethylcyanide to trigermylgermylcyanide. Since these compounds have not yet been synthesised, we have successfully compared the predicted parameters with related molecules for which results have been published in the literature. [Copyright &y& Elsevier]

Abstract: Theoretical methods have been employed to investigate the structural, spectroscopic and energetic properties of difluoro(germylthio)phosphine in the C s symmetry in the gas phase. The levels of theory used are MP2 and DFT/B3LYP and the basis set used for all atoms is 6-311G(d,p). The computed structural parameters, namely, bond lengths and bond angles and spectroscopic parameters, namely, infrared frequencies, Raman activities and NMR chemical shifts have been compared with experimental data reported in literature. The structure of this compound has been analysed using natural bond orbital approach. Both the ab initio methods perform satisfactorily when the predicted and experimental parameters are compared. We have extended this study, using the same methods and basis set, to the selenium analogue, namely, difluoro(germylseleno)phosphine for which literature is elusive. The MP2/6-311G(d,p) geometrical parameters for difluoro(germylseleno)phosphine are: r(P–Se)=2.270, r(Ge-Se)=2.386, r(P–F)=1.604, r(Ge–H)=1.530Å, ∠(Ge–Se–P)=91.4, ∠(F–P–F)=96.7, ∠(Se–P–F)=99.9 and ∠(Se–Ge–H)=109.5°. Apart from these, we have also studied the energetic parameters for their synthesis. The results indicate that formation of the sulphur-containing compound is favoured thermodynamically. [Copyright &y& Elsevier]

The Schiff base, 4-[3-(4-methoxy-phenyl)-allylideneamino]-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one (TPMC/AAP) was synthesized by the condensation of 4-aminoantipyrine (4-amino-1,5-dimethyl-2-phenylpyrazole-3-one) and trans-para-methoxycinnamaldehyde (trans-3,4-methoxyphenyl-2-propenal) in dry methanol at 75 °C. The compound was characterized using elemental microanalysis, IR, NMR, UV spectroscopies and single-crystal X-ray crystallography. The X-ray structure determination shows that the Schiff base, (TPMC/AAP) is orthorhombic with the Pbca space group. The anti-microbial screening of the compound was carried out with Escherichia coli, Bacillus subtillis, Staphylococcus aureus, Pseudemonas aeruginosa, Candida albicans and Aspergillus niger using agar well diffusion method. The Schiff base possesses significant antimicrobial activity. The minimum inhibitory concentration (MIC) of the compound was also determined and the activity was compared with that of conventional drugs ciprofloxacin and ketoconazole. The compound (TPMC/AAP) showed varying activity against the cultured bacteria and fungi used. To complement the experimental data, density functional theory (DFT) was used to have deeper understanding into the molecular parameters and infrared spectra of the compound. [ABSTRACT FROM AUTHOR]

The optimized molecular structures, vibrational wavenumbers and corresponding vibrational assignments of the syn and anti conformers of 2-, 3- and 4-pyridine carboxaldehydes and their sulfur and selenium analogues were calculated using the density functional theory method employing the B3LYP functional with the 6-311++G(d,p) basis set and second order Møller-Plesset Perturbation Theory (MP2) method with the cc-pVDZ basis set. The calculations were adapted to the C symmetries of all ground state structures. The transition state arising from syn-anti isomerization was also modelled. All structures were fully optimized, and the geometries, rotational constants, dipole moments, charges, thermodynamic properties and energies are reported. Energies of the optimized structures were used to obtain the energy difference between the syn and anti conformers and the rotational barrier. The calculated vibrational wavenumbers were appropriately assigned to the various fundamental modes of vibrations. The Integral Equation Formalism Polarization Continuum Model was used to calculate the optimized geometry and the vibrational wavenumbers for all of the compounds in nine solvents: heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide and water. In addition, the LUMO, HOMO and energy band gap are also reported. The results indicate that the anti conformer is preferred with a rotational barrier of at least 19 kJ·mol. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Theoretical studies were performed on seven potential interstellar and circumstellar substituted cyanoacetylenes, Y(C C)CN [Y = C 2 H 5 , C 3 H 7 , C 4 H 9 , F, Cl, Br and CN]. Geometry optimizations were carried out using the DFT/B3LYP, the CCSD and CCSD(T) levels of theory. The cc-pVTZ basis set was used for all atoms. Frequency computations were also carried out at the same level of theory as for the optimization to check the nature of the stationary points. The molecular and spectroscopic parameters of the cyanoacetylenes were computed. An analysis of these parameters is in line with the satisfactory performance of the B3LYP/cc-pVTZ level compared to the golden standard, the CCSD(T) level. The theoretical data reported in this work should facilitate future identifications of these cyanoacetylenes in extraterrestrial locations. Plausible mechanisms for the formation of these molecules have been proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • All possible tautomers of hydantoin interconversions were investigated. • DFT B3LYP-D3(BJ)/aug-cc-pVTZ method was used to account for dispersion corrections. • Explicit water and ethanol have a catalytic effect on specific energy barriers. • Binding energies for hydantoin bound to water or ethanol were calculated. Hydantoin exhibits tautomerism and the interconversion among the tautomers was studied using theoretical methods in the gas phase and solvents (water or ethanol). The implicit solvation as well as one explicit solvent molecule with water or ethanol were investigated. The functional used was B3LYP-D3(BJ) and the basis set for all atoms was aug-cc-pVTZ. The results indicate that the electronic energy barriers in the gas phase and implicit solvation are in the range 50–90 kcal mol−1. However, explicit water is found to have a catalytic effect as the electronic energy barriers are lowered to 18–30 kcal mol−1. Explicit ethanol lowers the electronic energy barriers further by about 2 kcal mol−1. This study should be beneficial for the rational design and experiments involving hydantoin and water or ethanol as solvents. [ABSTRACT FROM AUTHOR]

The characterization of the seleno-sulfide-bromo systems and the isomerization process on the [H, S, Se, Br] potential energy surface were investigated using state-of-the-art theoretical methods. The CCSD(T) and the MP2 levels of theory were employed along with the series of correlation consistent basis sets extrapolated to the complete basis set (CBS) limit in the optimization of the geometrical parameters and computation of electronic energies. The relative stability, in kcal mol, at the CCSD(T)/CBS follows the trend: HSSeBr (0) > HSeSBr (9.51) > SSeHBr (24.02) > SeSHBr (25.42). This order was observed in the previous study of the [H, S, Se, Cl] species. The structural parameters and vibrational frequencies of the [H, S, Se, Br] species are reported. This research work should be helpful to experimentalists in order to gain insights into these novel heteroatom molecules. [ABSTRACT FROM AUTHOR]

The rhenium(V) complexes [ReCl 3 ( t -BuNC)(L)(PPh 3 )] ( 1 – 3 ) were isolated by the reaction of trans -[Re III Cl 3 ( t -BuNC)(PPh 3 ) 2 ] ( t -BuNC = tert -butyl isocyanide) with the ligands H 2 L (H 2 L = aniline ( 1 ), o -phenylenediamine ( 2 ), anthranilic acid ( 3 )). In all these complexes the dianionic ligands L are coordinated monodentately as the imide. However, unexpectedly, with 2-aminophenol the complexes [Re V Cl 2 ( t -BuNC)(L)(PPh 3 ) 2 ](ReO 4 ) ( 4 ) and the novel [Re III Cl 2 ( t -BuNC)(ibq)(PPh 3 ) 2 ] ( 5 ) (ibq − = 2-iminobenzoquinonate, the two-electron oxidized form of HL − ) were identified as the products. These complexes were characterized by single crystal X-ray crystallography, 1 H NMR spectrometry, IR and electronic spectroscopy, and cyclic voltammetry. To complement the experimental data, density functional theory (DFT) and time-dependent DFT methods were used to have a deeper understanding into the molecular parameters and infrared and electronic spectra of these complexes. [ABSTRACT FROM AUTHOR]

The reaction of the rhenium(V) complex cis-[ReO2I(PPh3)2] with 2-aminothiophenol (H2atp), benzene-1,2-dithiol (H2tdt) and 2-hydroxybenzenethiol (H2otp) led to the formation of the rhenium(III) complexes [Re(Hatp)(ibsq)2]·OPPh3, [Re(sbsq)3]·OPPh3 and [Re(obsq)3]·OPPh3 (ibsq=2-iminothiobenzosemiquinonate, sbsq=1,2-dithiobenzosemiquinonate, obsq=2-hydroxothiobenzosemiquinonate) respectively. These paramagnetic complexes were characterized by single crystal X-ray crystallography, 1H NMR spectrometry, IR and electronic spectroscopy, and cyclic voltammetry. To complement the experimental data, density functional theory (DFT) and time-dependent DFT were successfully used to investigate the structural, molecular, infrared and electronic spectra of these three complexes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chalcogen surface additives boost the catalytic activity of Pt (1 1 1) surfaces. • S and Se surface additives are better catalytic activity boosters. • Dehydrogenation proceeds with or without indoline as an intermediate. • All the adsorbates stably adsorb on the surfaces with additives. Liquid organic hydrogen carrier (LOHC) systems have gained serious traction of late due to their potential application in the envisaged hydrogen economy. This is mainly because LOHCs can undergo reversible dehydrogenation in the presence of a catalyst. Using density functional theory calculations with van der Waals corrections, the role of chalcogens (S, Se and Te) as surface additives, in boosting the catalytic activity of Pt (1 1 1) surface, was investigated for the dehydrogenation of the LOHC system, octahydroindole to indole. The calculated adsorption energies indicate that octahydroindole (the hydrogen rich form (LOHC+)) and indole (the hydrogen lean form (LOHC−)) stably adsorbs on the Pt (1 1 1) surface(s) in the presence of chalcogen surface additives. The S and Se atoms were found to be better catalytic activity boosters in lowering the calculated reaction energy for dehydrogenating octahydroindole to indole than the Te atom. For all the considered chalcogen surface additive species, the calculated reaction energies indicate that the dehydrogenation of octahydroindole to indole can proceed either with or without indoline as a reaction intermediate. [ABSTRACT FROM AUTHOR]