Theoretical study of interactions between 1-alkyl-3-methyimidazolium tetrafluoroborate and dibenzothiophene: DFT,NBO, and AIM analysis

Density functional theory is employed to study the interaction energies between dibenzothiophene (DBT) and 1-alkyl-3-methylimidazolium tetrafluoroborate ([C _n mim]⁺[BF₄]^?). The structures of DBT, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim]⁺[BF₄]^?), 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]+[BF₄]?), 1-hexyl-3-methylimidazolium tetrafluoroborate ([C₆mim]⁺[BF₄]^?), 1-octyl-3-methylimidazolium tetrafluoroborate ([C₈mim]⁺[BF₄]^?), [C₂mim]⁺[BF₄]^?–DBT, [C₄mim]⁺[BF₄]^?–DBT, [C₆mim]⁺[BF₄]^?–DBT and [C₈mim]⁺[BF₄]^?–DBT systems are optimized systematically at the B3LYP/6-31G(d,p) level, and the most stable geometries are obtained by NBO and AIM analyses. The results indicate that DBT and imidazolium rings of ionic liquids are parallel to each other. It is found that the [BF₄]^? anion prefers to be located close to a C1–H9 proton ring in the vicinity of the imidazolium ring and the most stable gas-phase structure of [C _n mim]⁺[BF₄]^? has four hydrogen bonds between [C _n mim]+ and [BF₄]?. There are hydrogen bonding interactions, π–π and C–H–π interactions between [C₈mim]⁺[BF₄]^? and DBT, which is confirmed by NBO and AIM analyses. The calculated interaction energies for the studied ionic liquids can be used to interpret a better extracting ability of [C₈mim]⁺[BF₄]^? to remove DBT, due to stronger interactions between [C₈mim]⁺[BF₄]^? and DBT, in agreement with the experimental results of dibenzothiophene extraction by [C _n mim]⁺[BF₄]^?.     

Molecular structure, vibrational, UV and NBO analysis of 4-chloro-7-nitrobenzofurazan by DFT calculations

In the present work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of 4-chloro-7-nitrobenzofurazan (NBD-Chloride). The FT-IR (400-4000 cm(-1)) and FT-Raman spectra (50-4000 cm(-1)) of NBD-Chloride were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of NBD-Chloride in the ground-state have been calculated by using the density functional B3LYP method with 6-311++G (d, p) as higher basis set. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) result in DMSO and CDCl3 solvents complements with each other. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Finally the calculation results were applied to simulate infrared and Raman spectra of the title compound which show good agreement with observed spectra.     

HCCO自由基与水分子氢键复合物的从头算研究

在MP2/aug-cc-pvdz水平下,对二体氢键复合物H2O…HCCO(Ⅰ)和HCCO…H2O(Ⅱ)以及三体氢键复合物(H2O)2…HCCO(Ⅲ),H2O…H2O…HCCO(Ⅳ)和H2O…HCCO…H2O(Ⅴ)的几何和相互作用能进行了计算.轨道分析表明Ⅲ中HCCO中的H(1),C(2)通过2个氢键与2个水分子形成了环...     

DFT computations,vibrational spectra,monomer, dimer,NBO and NMR analyses of antifungal agent: 3,5-Dibromosalicylic acid

The experimental and theoretical study on the structures and vibrations of 3,5-dibromosalicylic acid (DBSA) are presented. The FT-IR and FT-Raman of the title compound have been recorded. The molecular structures, vibrational wavenumbers, infrared intensities, Raman activities were calculated. The energies of DBSA are obtained for all the eight conformers from density functional theory with 6-311++G(d,p) basis set calculations. From the computational results, C1 or C5 forms are identified as the most stable conformers of DBSA. The spectroscopic and theoretical results are compared with the corresponding properties for DBSA monomer and dimer of C1 (or C5) conformer. Intermolecular hydrogen bonds are discussed in dimer structure of the molecule. NBO analysis is useful to understand the intramolecular hyperconjugative interaction between lone pair O9 and C7O8. The calculated HOMO–LUMO energies reveal charge transfer occurs within the molecule. The polarizability, first hyperpolarizability, anisotropy polarizability invariant has been computed using quantum chemical calculations. The isotopic chemical shift computed by ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the DBSA molecule, calculated using the gauge invariant atomic orbital (GIAO) method, also shows good agreement with experimental observations.     

DFT study of the electronic, vibrational, and optical properties of SnO2

We report results on the electronic, vibrational, and optical properties of SnO₂ obtained using first-principles calculations performed within the density functional theory. All the calculated phonon frequencies, real and imaginary parts of complex dielectric function, the energy-loss spectrum, the refractive index, the extinction, and the absorption coefficients show good agreement with experimental results. Based on our calculations, the SnO₂ electron and hole effective masses were found to be strongly anisotropic. The lattice contribution to the low-frequency region of the SnO₂ dielectric function arising from optical phonons was also determined resulting the values of ? _1⊥ ^latt (0) = 14.6 and ? _1∥ ^latt (0) = 10.7 for directions perpendicular and parallel to the tetragonal c-axis, respectively. This is in excellent agreement with the available experimental data. After adding the electronic contribution to the lattice contribution, a total average value of ?₁(0) = 18.2 is predicted for the static permittivity constant of SnO₂.     

A quantum topological study of the electron density in monomers and dimers of acyclic azathiens with aromatic substituents

A theoretical study of electron density, ρ(r), and the Laplacian (ab initio, DFT B3LYP/6-31G(d, p) basis set) has been carried out for nine molecules of azathiens with aryl substituents (Ar-N=S=N-Ar₁) and for sixteen dimers corresponding to typical arrangements of neighboring molecules in the crystal structures of Ar-N=S=N-Ar₁. A dependence was established of the values of the electron density at (3, ?1) critical points in the area of inter-stack and intra-stack atom-atom contacts on the internuclear distance.     

Comparative DFT study of van der Waals complexes: rare-gas dimers, alkaline-earth dimers, zinc dimer, and zinc-rare-gas dimers

Recent interest in the application of density functional theory prompted us to test various functionals for the van der Waals interactions in the rare-gas dimers, the alkaline-earth metal dimers, zinc dimer, and zinc-rare-gas dimers. In the present study, we report such tests for 18 DFT functionals, including both some very recent functionals and some well-established older ones. We draw the following conclusions based on the mean errors in binding energies and complex geometries: (1) B97-1 gives the best performance for predicting the geometry of rare-gas dimers, whereas M05-2X and B97-1 give the best energetics for rare-gas dimers. (2) PWB6K gives the best performance for the prediction of the geometry of the alkaline-earth metal dimers, zinc dimers, and zinc-rare-gas dimers. M05-2X gives the best energetics for the metal dimers, whereas B97-1 gives the best energetics for the zinc-rare-gas dimers. (3) The M05 functional is unique in providing good accuracy for both covalent transition-metal dimers and van der Waals metal dimers. (4) The combined mean percentage unsigned error in geometries and energetics shows that M05-2X and MPWB1K are the overall best methods for the prediction of van der Waals interactions in metal and rare-gas van der Waals dimers.     

Theoretical study of the structures and vibrational spectra of the hydrogen-bonded systems of 4-cyanophenol with N-bases

The structural and vibrational features of the hydrogen bonded complexes of 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) with one and two 4-CNPhOH molecules have been studied extensively by ab initio SCF/6-31G(d,p) and BLYP calculations with various basis sets: 6-31G(d,p), 6-31+G(d,p) and 6-31++G(d,p). Full geometry optimization was made for the complexes studied. The nature of the hydrogen bonding and the influence of the hydrogen bonding on the structural and vibrational characteristics of the monomers have been investigated. The corrected values of the dissociation energy for the hydrogen-bonded complexes have been calculated in order to estimate their stability. The calculated values of the dissociation energy per phenol molecule indicate that the complex: TBD: 4-CNPhOH (1:1) is more stable than the complex: TBD: 4-CNPhOH (1:2). The changes in the structural and vibrational characteristics upon hydrogen bonding depend on the strength of the hydrogen bonds. In agreement with the experiment, the calculations show that the complexation between TBD and 4-CNPhOH leads to considerably changes in the vibrational characteristics of the stretching O-H vibration. The vibrational frequency of the O-H stretching vibration is shifted to lower wave numbers upon hydrogen bonding. The predicted frequency shifts Deltanu(O-H) for the complexes--TBD: 4-CNPhOH (1:1) and TBD: 4-CNPhOH (1:2) are in the range from -190 cm(-1) to -586 cm(-1). In the same time the IR intensity of the O-H stretching vibration increases dramatically in the hydrogen-bonded complexes.     

Control of a photoswitching chelator by metal ions: DFT,NBO, and QTAIM analysis

Ability of aroylhydrazones to change conformation upon interaction with light makes them promising candidates for molecular switches. Isomerization can be controlled through complexation with selected metal ions which bind with different affinity. N′‐[1‐(2‐hydroxyphenyl)ethyliden]iso‐nicotinoylhydrazide (HAPI) is an example of a dual‐wavelenght photoswitching molecule, whose complexation with metal ions was recently experimentally investigated (Franks et al. J. Inorg. Chem. 2014, 53, 1397). In this contribution, complexes between HAPI and K⁺, Ca²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Cu⁺, Cu²⁺, and Zn²⁺ ions were investigated using Density Functional Theory, Natural Bond Order analysis, and Quantum Theory of Atoms in Molecules. The most important parameters that determine complex stability are found to be ion radius and charge transferred from ligands to the ion: smaller ion radii and larger CT values characterize formation of more stable complexes. Our results explain experimentally observed effect of different metal ions on photoisomerization through determination of metal ion affinity (MIA): photoisomerization is inhibited if MIA exceeds 100 kcal/mol; for MIA between 50 and 100 kcal/mol excess of metal ions prevents isomerization, whereas in case of MIA below 50 kcal/mol metal ions have no influence on light–HAPI interaction. © 2015 Wiley Periodicals, Inc.     

A DFT study of the vibrational spectra of 1-, and 2-nitrotriphenylene

The infrared (IR) and Raman spectra, and intensities of triphenylene, 1-, and 2-nitrotriphenylene were investigated by the density functional theory (DFT, B3LYP method) with 6-311+G** basis set. Normal mode assignments are proposed with particular emphasis on the nitro group vibrations. Compared to 2-nitrotriphenylene (2-NTRP) 1-nitrotriphenylene (1-NTRP) is predicted to show asymmetric nitro stretches at higher frequencies. Through the vibrational study, the structure–spectroscopic relationships of these nitro polycyclic aromatic hydrocarbons (nitro-PAHs) are made, and possible insights into their differential mutagenic potencies correlated. The geometrical distortions of the TRP structure upon nitro group substitution and correlations between structural parameters and vibrational data as well as structure–function relationships related to the mutagenicity of this important class of polycyclic aromatic hydrocarbons are discussed.     

DFT-based molecular modeling, NBO analysis and vibrational spectroscopic study of 3-(bromoacetyl)coumarin

The NIR-FT Raman and FT-IR spectra of 3-(bromoacetyl)coumarin (BAC) molecule have been recorded and analyzed. Density functional theory (DFT) calculation of two BAC conformers has been performed to find the optimized structures and computed vibrational wavenumbers of the most stable one. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Characteristic vibrational bands of the pyrone ring and methylene and carbonyl groups have been identified. The lowering of HOMO–LUMO energy gap clearly explains the charge transfer interactions taking place within the molecule.     

Ab initio and DFT studies of the vibrational spectra of hydrogen-bonded PhOH...(H2O)4 complexes

The vibrational characteristics (vibrational frequencies and infrared intensities) for the hydrogen-bonded complex of phenol with four water molecules PhOH...(H2O)4 (structure 4A) have been predicted using ab initio and DFT (B3LYP) calculations with 6-31G(d,p) basis set. The changes in the vibrational characteristics from free monomers to a complex have been calculated. The ab initio and B3LYP calculations show that the observed four intense bands at 3299, 3341, 3386 and 3430 cm(-1) can be assigned to the hydrogen-bonded OH stretching vibrations in the complex PhOH...(H2O)4 (4A). The complexation leads to very large red shifts of these vibrations and very strong increase in their IR intensity. The predicted red shifts for these vibrations with B3LYP/6-31G(d,p) calculations are in very good agreement with the experimentally observed. It was established that the phenolic OH stretching vibration is the most sensitive to the hydrogen bonding. The predicted red-shift with the B3LYP/6-31G(d,p) calculations for the most stable ring structure 4A (-590 cm(-1)) is in better agreement with the experimentally observed than the red-shift, predicted with SCF/6-31G(d,p) calculations. The magnitude of the wavenumber shift is indicative of relatively strong OH...H hydrogen-bonded interaction. The complexation between phenol and four water molecules leads to strong increase of the IR intensity of the phenolic OH stretching vibration (up to 38 times).     

Structure, stability and vibrational spectrum of the hydrogen-bonded complex between HNO3 and H2O. Ab initio and DFT studies

The structure, stability and vibrational spectrum of the binary complex between HONO2 and H2O have been investigated using ab initio calculations at SCF and MP2 levels with different basis sets and B3LYP/6-31G(d,p) calculations. Full geometry optimization was made for the complex studied. It was established that the hydrogen-bonded H2O...HONO2 complex has a planar structure. The corrected values of the dissociation energy at the SCF and MP2 levels and B3LYP calculations are indicative of relatively strong OH...O hydrogen-bonded interaction. The changes in the vibrational characteristics (vibrational frequencies and infrared intensities) arising from the hydrogen bonding between HONO2 and H2O have been estimated by using the ab initio calculations at SCF and MP2 levels and B3LYP/6-31G(d,p) calculations. It was established that the most sensitive to the complexation is the stretching O-H vibration from HONO2. In agreement with the experiment, its vibrational frequency in the complex is shifted to lower wavenumbers. The predicted frequency shift with the B3LYP/6-31G(d,p) calculations (-439 cm(-1)) is in the best agreement with the experimentally measured (-498 cm(-1)). The intensity of this vibration increases dramatically upon hydrogen bonding. The ab initio calculations at the SCF level predict an increase up to five times; at the MP2 level up to 10 times and the B3LYP/6-31G(d,p) predicted increase is up to 17 times. The good agreement between the predicted values of the frequency shifts and those experimentally observed show that the structure of the hydrogen-bonded complex H2O...HONO2 is reliable.     

Study of noncovalent interactions of end-caped sulfur-doped carbon nanotubes using DFT,QTAIM, NBO and NCI calculations

In the current study, the interactions of carbon nanotube and sulfur-doped carbon nanotubes (SCNTs) with methanol, methanethiol, water and dihydrogen sulfide at on-body and dead-end positions of nanotubes have been studied. Interaction energies in the gas and solvent (via PCM model) were calculated using density functional theory calculations. Atomic charges, interaction energies, electron densities and their Laplacians at bond critical points have been calculated. Moreover, noncovalent interaction isosurfaces have been visualized using NCI index calculations. Interactions in gaseous phase were more favorable than those in solvent phase, and among considered solvents (benzene, chloroform and cyclohexane), cyclohexane showed the most preferred interactions. In addition, oxygen-bearing molecules (methanol and water) showed more favorable interactions compared with sulfur-bearing ones. NBO analyses revealed the stronger donor–acceptor interactions with methanol and methanethiol. QTAIM calculation results indicated the reasonable electron densities at BCPs, and the Laplacians of electron densities showed ionic-like (closed shell) interactions. Moreover, isosurfaces of these interactions were also studied to depict the interaction surfaces, and DOS plots for SCNTs were obtained to define their HOMO–LUMO levels and electric conduction properties. The increasing of the global softness and decreasing of total hardness was resulted by sulfur doping of nanotubes, which causes the heterodoped nanotubes to become less electrophilic species.     

Structure and vibrational spectrum of the hydrogen-bonded system between 4-tert-butylphenol and N-bases: Ab initio and DFT studies

The structural and vibrational characteristics of the hydrogen-bonded system between 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) and 4-tert-butylphenol have been investigated employing ab initio and DFT calculations at different basis sets. The calculations show that the optimized structure of the studied system is cyclic. The corrected values of the dissociation energy for the hydrogen-bonded complex have been calculated in order to estimate its stability. The influence of the hydrogen bonding on the properties of the monomers (TBD and 4-tert-butylphenol) has been investigated. The hydrogen bonding between TBD and 4-tert-butylphenol leads to changes in the structural (bond lengths and angles) and vibrational (vibrational frequencies and infrared intensities) characteristics of the monomers. It was established that the TBD molecule is considerably deformed upon hydrogen bonding, while the deformation of the 4-t-BuPhOH is smaller. In agreement with the experiment, the calculations show that the stretching O-H vibration from 4-tert-butylphenol is shifted to lower frequency upon hydrogen bonding. The predicted frequency shift Deltanu(O-H) (-338cm(-1)) is in very good agreement with the experimentally observed (-351cm(-1)). In the same time the IR intensity of the nu(O-H) increases dramatically in the hydrogen-bonded system.     

Molecular structure, vibrational spectra and NBO analysis of phenylisothiocyanate by density functional method

The molecular geometry, vibrational frequencies and NBO analysis of phenylisothiocyanate (PITC) in the ground state have been calculated by using density functional theory calculation (B3LYP) with 6-311++G(d,p) basis set. The optimized geometrical parameters obtained by DFT calculations are in good agreement with experimental values. Comparison of the observed fundamental vibrational frequencies of the PITC and calculated result by density functional theory (B3LYP) indicates B3LYP is superior for molecular vibrational problems. The entropy of the title compound was also performed at HF/B3LYP/6-311++G(d,p) levels of theory. Natural bond orbital (NBO) analysis of title molecule is also carried out. A detailed interpretation of the IR and Raman spectra of PITC is reported on the basis of the calculated potential energy distribution (PED). The theoretical spectrogram for IR spectrum of the title molecule has been constructed.     

On the correlation between bond-length change and vibrational frequency shift in hydrogen-bonded complexes: a computational study of Y...HCl dimers (Y = N2, CO, BF)

The H-Cl bond-length change and the harmonic vibrational frequency shift of the H-Cl stretch on formation of the linear isoelectronic Y...H-Cl complexes (Y = N(2), CO, BF) have been determined by ab initio computations at different levels of theory. These shifts are in agreement with predictions from a model based on perturbation theory and involving the first and second derivatives of the interaction energy with respect to displacement of the H-Cl bond length from its equilibrium value in the isolated monomer. At the highest level of theory, blue shifts were obtained for BF...HCl and CO...HCl, while red shifts were obtained for FB...HCl, OC...HCl, and N(2)...HCl. These vibrational characteristics are rationalized by considering the balance between the interaction energy derivatives obtained from the perturbative model. The widely believed correlation between the bond-length change and the sign of the frequency shift obtained on complexation is discussed and found to be unreliable.     

pH-dependent Raman study of pyrrole and its vibrational analysis using DFT calculations

Raman spectra of pyrrole in aqueous medium at different pH values, 2.5, 5.5, 7.5 and 10.5 were recorded in the two spectral regions, 1,040-1,160 cm(-1) and 3,300-3,360 cm(-1) and pH dependence of the linewidth, peak position and intensity of the Raman bands corresponding to the ring breathing and symmetric nu(N-H) stretching modes were examined. A linear pH dependence of the peak positions for the ring breathing mode and a maximum at nearly neutral pH (7.5) for the symmetric nu(N-H) normal mode is observed, whereas the linewidth (FWHM) shows almost no variation with the change of pH. A slight decrease in the wavenumber position of the nu(N-H) mode at pH value >7.5 indicates that the influence of deprotonation is small, which results from a weak interaction between the reference molecule and the surrounding environment. The density functional theory (DFT) calculations were made primarily to obtain the optimized geometry and vibrational spectra of pyrrole in the ground electronic state using B3LYP functional and the highest level basis set 6-311++G(d,p). The assignments of the normal modes of pyrrole were made on the basis of potential energy distribution (PED). The calculations were also performed on protonated and deprotonated structures of pyrrole.     

Intramolecular hydrogen bonds in the sulfonamide derivatives of oxamide, dithiooxamide, and biuret. FT-IR and DFT study, AIM and NBO analysis

The hydrogen bonding in [(1-arylsulfonylamino-2,2,2-trichloro)ethyl]biuret 1, [(1-arylsulfonylamino-2,2,2-trichloro)ethyl]oxamide 2, and [(1-arylsulfonylamino-2,2,2-trichloro)ethyl]dithiooxamide 3, the sulfonamide derivatives of biuret 4, oxamide 5, and dithiooxamide 6, has been studied by molecular spectroscopy and DFT theoretical calculations including frequency calculations, at the B3LYP/6-311+G(d,p) level of theory. The analysis of the CO?HN and CS?HN intramolecular hydrogen bonds closing the five- and six-membered rings employing the atoms-in-molecules (AIM) method using the MP2(full)/6-311++G(d,p) wave functions has shown that their stability is increased in comparison to the original molecules and is much higher in the thiocarbonyl compounds. The results of the AIM and the NBO analysis of donor-acceptor interactions are in good agreement with each other and with the experimental FT-IR spectroscopy data.     

Theoretical study of the equilibrium structure, vibrational spectrum, and thermochemistry of the peroxynitrate CF2BrCFBrOONO2

The results of a theoretical study of the molecular structure and conformational mobilities of the peroxynitrate CF(2)BrCFBrOONO(2) and its radical decomposition product CF(2)BrCFBrOO are reported in this paper. The most stable structures were calculated from ab initio G3(MP2)B3 and G4(MP2) methods and from density functional theory at the B3LYP/6-311+G(d) and B3LYP/6-311+G(3df) levels of theory. The equilibrium conformation of CF(2)BrCFBrOONO(2) indicates that the bromine atoms lie in position anti to each other and possess a COON dihedral angle of 114°. A quantum statistical analysis shows that about 40% of the internal rotors can freely rotate at room temperature. Our best values for the standard enthalpies of formation of CF(2)BrCFBrOONO(2) and CF(2)BrCFBrOO at 298 K obtained from isodesmic reactions at the G3(MP2)//B3LYP/6-311+G(3df) level of theory are -144.7 and -127.0 kcal mol(-1). From these values and the enthalpy of formation of the NO(2) radical, a CF(2)BrCFBrOO-NO(2) bond dissociation enthalpy of 26.0 ± 2 kcal mol(-1) was estimated.