Equilibrium Geometric Parameters Research Articles

Characterization, DFT calculations and antimicrobial assays of some novel nanoparticles mixed ligand complexes of 5-cyano-6-phenyl-2-thiouracil in presence of 1,10-phenanthroline

Some trivalent (Cr(III), Fe(III)) and divalent (Co(II), Ni(II), Cu(II) Zn(II)) combined with synthesized 5-cyano-6-phenyl-2-thiouracil (H2CPT) in presence 1,10-phenanthroline monohydrate (Phen) to produce crystalline and semi-crystalline nanoparticles mixed ligand metal complexes. The separated nanoparticles complexes were investigated by physicochemical, spectroscopic techniques (FT-IR, UV–Vis. and 1H NMR), X-ray powder diffraction (XRD) and thermal analyses (TG-DTG-DTA). The metal complexes were ionic with 1:2 electrolytes for divalent elements and 1:3 electrolytes for trivalent elements. The FT-IR spectra indicated that H2CPT and Phen functioning as bidentate ligand binding to the metal ions via oxygen and nitrogen of cyano group of H2CPT and through two nitrogen of Phen. According to the magnetic moment and UV–vis. spectra the complexes were identified as octahedral geometries. The XRD analysis of the prepared compounds revealed that H2CPT and the complexes of Cr(III), Fe(III), Co(II) and Ni(II) display semi-crystalline peaks while, Cu(II) and Zn(II) complexes were crystalline in nature. The mechanism of the thermal degradation was identified and the kinetic parameters of the disintegration stages were assessed using Coats-Redfern (CR) and Horowitz-Metzger (HM) methods. DFT computations were used to calculate equilibrium geometric parameters and the lowest energy model structures. H2CPT, Phen and their metal complexes were examined for effectiveness towards two G(+), two G(-) bacteria and two fungi. Co(II) complex was significant, highly significant and very highly significant against all tested bacterial and fungi strains compared with H2CPT, Phen, references standard control and all other complexes.

A quantum-chemically supported classical approach to assessing the vibrational contribution to the thermal expansion of molecules. Example of LaI3

А dynamic vibrational task has been solved with taking into account the interaction of vibrational coordinates on the base of the calculated PES. The vibrational level energies and corresponding wave functions of LaI3 molecule have been determined by the solution of three-dimensional Schrödinger equations. Theoretical calculations were performed by the DFT/PBE0, DFT/B3LYP and MP2 methods using relativistic effective pseudopotentials and a good quality basis sets for inner and outer atomic shells. Six-dimensional PES was numerically calculated by the DFT/PBE0 approach. Available gas-phase electron diffraction (GED) data were simulated by the original methodology based on the full dimensional PES. A good agreement between experimental and theoretical thermal average structural parameters supports the reliability of the theoretical data and the efficiency of the methodology implemented. It is shown that the standard approaches based on the use of the harmonic approximation, to calculate of the vibrational corrections necessary for the interpretation of GED results, at high temperatures lead to either significantly overestimated or underestimated values of equilibrium geometrical parameters. An analysis of the anharmonic vibrational levels obtained indicates the absence of Fermi resonances and the suitability of the harmonic approximation for describing fundamental vibrational transitions.

Solvated State of Ethylenediamine in Nonaqueous Solvents, According to Quantum Chemical Data

Quantum chemical modeling is used to study the equilibrium geometric parameters and atomic charges in molecules of ethylenediamine (En) in the free state, methanol (MeOH), acetonitrile (AN), N,N‑dimethylformamide (DMF) and dimethylsulfoxide (DMSO), along with the Gibbs energies and enthalpies of amine solvation in the considered solvents. It is found that the conformational state of En is approximately the same in each solvent. In aprotic solvents, the solvation of En proceeds mainly because of the universal type of interactions between amine molecules and solvent molecules; in methanol, solvation energy of En and the solvate’s stability are determined by both universal and specific types of solute–solvent interactions with the contribution from the universal type of interactions predominating.

VIBRATIONAL SPECTROSCOPIC INVESTIGATION AND MOLECULAR STRUCTURE OF A 5α-REDUCTASE INHIBITOR: FINASTERIDE

By way of Density Functional Theory (DFT)-based computational methods with commercially available software, the computational work of which about the molecular properties, the vibrational modes and vibrational frequencies of finasteride were accomplished for the first time. In order to gain a deeper and more thorough understanding of the molecular structure and infrared spectrum of finasteride, the equilibrium geometry harmonic vibrational frequencies and geometric parameters (bond lengths, bond angles and dihedral angles) were calculated by Generalized Gradient Approximations (GGAs) with five different density functional methods (PBE, RPBE, HCTH, PW91 and BLYP), using Material Studio 8.0 program. Theoretical vibrational frequencies and theoretical optimized geometric parameters were compared with the corresponding experimental data, which concluded that the GGA/PW91 method were shown to be in a good agreement with the results of experiment. In addition, the highest occupied molecular orbital (HOMO) energies, the lowest unoccupied molecular orbital (LUMO) energies and electron density isosurface calculations were done with an aim at a better understanding of the stability and reactivity of the molecule, indicating that the alkene and lactam conjugated system on the ring A is more likely to interact with other species. And, the atomic charge distribution was also calculated to understand the charge effect caused by electronegative atoms, which shows that the possible active-sites in chemical reactions are N1 and O1.

MOLECULAR STRUCTURE AND QUANTUM CHEMICAL CALCULATIONS 4-ETHYL-5-(2-HYDROXYPHENYL)-1,2,4-TRIAZOL-3-THIONE

The article is devoted to the study of the spatial structure of 4-ethyl-5-(2-hydroxyphenyl)-1,2,4-triazole-3-thione. The molecular and crystalline structure was determined by x-ray diffraction analysis. Data on thespatial structure and crystal packing of the molecule are presented. It is established that phenyl and triazole rings areflat. Due to hydrogen bonds, the molecules in the crystal form three-dimensional networks. The results of an X-raydiffraction study were deposited at the Cambridge Center for Crystal Structural Data. The structure of thesynthesized 1,2,4-triazole was studied by 1H NMR spectroscopy. When analyzing the 1H NMR spectrum of thecompound, characteristic signals of the protons of the aromatic ring are observed. The value of the chemical shift andthe integrated signal intensity are determined. A quantum chemical study of 4-ethyl-5-(2-hydroxyphenyl)-1,2,4-triazole-3-thione was carried out by the DFT method using the B3LYP exchange-correlation functional incombination with the Danning basic set cc-pVDZ. The molecular characteristics of the compound, such as totalelectron energy, rotational constants, dipole moment and contributions, and thermodynamic functions, are predicted.The equilibrium geometric parameters of the 4-ethyl-5-(2-hydroxyphenyl)-1,2,4-triazole-3-thione molecule weredetermined. The performed analysis of the spatial configuration and molecular parameters showed a qualitativecorrespondence between the crystalline and gas-phase structures of the molecule, while it was noted that the maindifference is observed in the relative orientation of six- and five-membered cycles.

On Sulfur Reduction Mechanism in Li-S Cells. Formation of Li2S8

The results of quantum-chemical simulation of the first stage of the electrochemical reduction of sulfur S8 to Li2S8 are presented. The thermal effects of the formation of all possible intermediates for the electrochemical reduction of sulfur to lithium octasulfide are estimated. The sequence of these elementary reactions is established. The structure and properties of the resulting intermediates are characterized in AIMAll programm. Quantum chemical calculations were performed using the Gaussian09 software package. The search for equilibrium geometrical parameters and the calculation of the energy characteristics of sulfur S8 and possible intermediate products of its reduction were carried out without taking into account solvation. The optimization procedure and the calculation of the vibrational problem were performed using the TPSS/aug-cc-pVTZ method for the correct description of anions. Electronic correlation was taken into account by a single point calculation at the level of perturbation theory of combined CCSD clusters (CCSD/aug-cc-pVTZ). Structures with an unpaired electron were calculated using the unlimited Hartree Fock/Kohn Sham method.To construct the initial structures of the intermediates of the sulfur reduction reaction to lithium octasulfide containing lithium cations, quantitative estimates of the electrostatic potential were carried out in MultiWFN software package. Two parallel processes with the participation of the S8 molecule was simulated: electron gain and the formation of complexes with lithium cations. According to the calculations, a deformation of the S8 structure is observed when electrons are added. First electron gain reaction leads to DS8 - anion formation. S2-S8 and S4-S5 bond lengths increases compared to S8 molecule by 0.285 Å; S1-S2 and S5-S6 bonds are shortened by 0.022 Å; S3-S4 and S7-S8 bonds are shortened by 0.017 Å; S1-S3 and S6-S7 increase by 0.014 Å. When a second electron is added, the tendency to change bond lengths remains, but the structure becomes more symmetrical. Thus, in the DS8 - anion there are 4 pairs of equivalent bonds, and in the SS8 -2 and TS8 -2 dianions, one pair of enlarged bonds and 4 pairs of bonds shortened compared to the S8 molecule. In the case of dianions, the final product is a complex of two S4 - anions. The addition of lithium cations to the four states of sulfur SS8, DS8 -, SS8 -2 and TS8 -2 leads to the following changes: when adding the first Li+ cation to SS8, the initial symmetry of the sulfur ring does not change, the S-S bond length increases by 0.010 Å. The lithium atom forms four equivalent bonds with sulfur (Li-S) of 2.692 Å. The subsequent addition of the second lithium cation leads to the deformation of the structure and the violation of symmetry. The addition of lithium cations to the DS8 - and SS8 -2 anions leads to the breaking of one of the S-S bonds and the formation of Li-S bonds, while the polysulfide chain is not broken. In contrast to the DS8 - and SS8 -2 anions, in the TS8 -2 anion, changes in the initial sulfur ring are more significant - when the first lithium cation is added, two S-S bonds break to form a complex (S3-Li-S5)-2, and with the addition of two cations, a complex (S4-Li2-S4)-2 is formed. According to AIM analysis, the properties of the bonds of all the particles under study are established, in particular, the electron density (ρ) and the bond delocalization index (DI). Thus, in the S8 molecule, all bonds are equivalent since ρ and DI for all bonds are 0.131401 and 1.3, respectively. When an electron is accepted as a sulfur molecule, the strain of the S–S bonds is observed and, in addition to the bond lengths, the ρ and DI values change in a similar way. It is noteworthy that in the triplet form of the dianion, despite the fact that the length of the breaking S-S bond is longer than in the singlet form, DI is 0.2 more than in the singlet form, indicating a stabilizing factor. In the framework of the ideal gas model, the most probable reaction path for sulfur reduction was established based on thermodynamic calculations: the first act is the interaction of sulfur S8 with the Li+ cation; the second is the electron gain by the particle SLiS8 +; the third step is the electron gain by the DLiS8 - and the final stage is the formation of the Li2S8 molecule. This work was financially supported by the Russian Science Foundation (project No 17-73-20115 ), Russia. Figure 1

Vibrational study and Natural Bond Orbital analysis of serotonin in monomer and dimer states by density functional theory

The vibrational spectral analysis of Serotonin and its dimer were carried out using the Fourier Transform Infrared (FTIR) and Raman techniques. The equilibrium geometrical parameters, harmonic vibrational wavenumbers, Frontier orbitals, Mulliken atomic charges, Natural Bond orbitals, first order hyperpolarizability and some optimized energy parameters were computed by density functional theory with 6-31G(d,p) basis set. The detailed analysis of the vibrational spectra have been carried out by computing Potential Energy Distribution (PED, %) with the help of Vibrational Energy Distribution Analysis (VEDA) program. The second order delocalization energies E(2) confirms the occurrence of intramolecular Charge Transfer (ICT) within the molecule. The computed wavenumbers of Serotonin monomer and dimer were found in good agreement with the experimental Raman and IR values.

Thiobenzamide: Structure of a free molecule as studied by gas electron diffraction and quantum chemical calculations

The equilibrium (re) molecular structure of thiobenzamide along with rh1 structure has been determined in gas phase using gas electron-diffraction (GED) at about 127 °C and quantum-chemical calculations (QC). Rovibrational distance corrections to the thermal averaged GED structure have been computed with anharmonic force constants obtained at the MP2/cc-pVTZ level of theory. According to the results of GED and QC thiobenzamide exists as mixture of two non-planar enantiomers of C1 symmetry. The selected equilibrium geometrical parameters of thiobenzamide (re, Å and ∠e, deg) are the following: (CS) = 1.641(4), (CN) = 1.352(2), (CC) = 1.478(9), (CC)av = 1.395(2), CCN = 114.7(5), CCS = 123.4(5), C2C1C7S = 31(4), C6C1C7N = 29(4). The structure of thiobenzamide in the gas phase is markedly different to that in the literature for the single crystal. The differences between the gas and the solid structures are ascribed to the presence of intermolecular hydrogen bonding in the solid phase.

Ionization of pyridine: Interplay of orbital relaxation and electron correlation.

The valence shell ionization spectrum of pyridine was studied using the third-order algebraic-diagrammatic construction approximation scheme for the one-particle Green's function and the outer-valence Green's function method. The results were used to interpret angle resolved photoelectron spectra recorded with synchrotron radiation in the photon energy range of 17-120 eV. The lowest four states of the pyridine radical cation, namely, 2A2(1a2-1), 2A1(7a1-1), 2B1(2b1-1), and 2B2(5b2-1), were studied in detail using various high-level electronic structure calculation methods. The vertical ionization energies were established using the equation-of-motion coupled-cluster approach with single, double, and triple excitations (EOM-IP-CCSDT) and the complete basis set extrapolation technique. Further interpretation of the electronic structure results was accomplished using Dyson orbitals, electron density difference plots, and a second-order perturbation theory treatment for the relaxation energy. Strong orbital relaxation and electron correlation effects were shown to accompany ionization of the 7a1 orbital, which formally represents the nonbonding σ-type nitrogen lone-pair (nσ) orbital. The theoretical work establishes the important roles of the π-system (π-π* excitations) in the screening of the nσ-hole and of the relaxation of the molecular orbitals in the formation of the 7a1(nσ)-1 state. Equilibrium geometric parameters were computed using the MP2 (second-order Møller-Plesset perturbation theory) and CCSD methods, and the harmonic vibrational frequencies were obtained at the MP2 level of theory for the lowest three cation states. The results were used to estimate the adiabatic 0-0 ionization energies, which were then compared to the available experimental and theoretical data. Photoelectron anisotropy parameters and photoionization partial cross sections, derived from the experimental spectra, were compared to predictions obtained with the continuum multiple scattering approach.

Structure and thermodynamic properties of cluster ions in saturated vapour over barium dibromide

The structure and thermodynamic properties of cluster ions detected earlier in saturated vapour over barium dibromide were studied theoretically. The equilibrium geometrical parameters and vibrational spectra were computed for the ions BaBr3−, Ba2Br3+, Ba3Br5+, Ba4Br7+ and Ba5Br9+; the DFT and MP2 methods with triple-zeta valence basis sets were used. The enthalpies of ion molecular reactions were obtained both theoretically through the total energies of participants and based on experimental data. The theoretical results were scrutinized with respect to methods of computation (DFT, MP2, and MP4). The enthalpies of formation ΔfHo(0) of the ions have been determined (in kJmol−1): −858±6 (BaBr3−); −293±10 (Ba2Br3+); −982±20 (Ba3Br5+); −1644±30 (Ba4Br7+); −2282±17 (Ba5Br9+).

Cluster ions in saturated vapor over barium difluoride: Structure and thermodynamic properties

Different cluster ions detected earlier in saturated vapor over barium fluoride have been studied here theoretically. The equilibrium geometrical parameters and vibrational spectra were obtained for the ions BaF3−, Ba2F3+, Ba3F5+, Ba4F7+, and Ba5F9+. The DFT/B3P86 and MP2 methods were implemented with the TZVP basis sets including the diffuse and polarized basis functions. Along with cluster ions, the dimer molecule Ba2F4 properties were examined; the existence of isomeric forms was confirmed and the relative concentration of the isomers was evaluated. The enthalpies of ion molecular reactions were obtained both theoretically and based on experimental data. The enthalpies of formation ΔfHo(0) of the species were determined (in kJmol−1): −1356±4 (BaF3−); −1039±12 (Ba2F3+); −2179±16 (Ba3F5+); −3277±35 (Ba4F7+); −4316±22 (Ba5F9+); −1859±7 (Ba2F4).

A Study of H2O2 with Threshold Photoelectron Spectroscopy (TPES) and Electronic Structure Calculations: Redetermination of the First Adiabatic Ionization Energy (AIE).

In this work, hydrogen peroxide has been studied with threshold photoelectron (TPE) spectroscopy and photoelectron (PE) spectroscopy. The TPE spectrum has been recorded in the 10.0-21.0 eV ionization energy region, and the PE spectrum has been recorded at 21.22 eV photon energy. Five bands have been observed which have been assigned on the basis of UCCSD(T)-F12/VQZ-F12 and IP-EOM CCSD calculations. Vibrational structure has only been resolved in the TPE spectrum of the first band, associated with the X̃(2)Bg H2O2(+) ← X̃(1)A H2O2 ionization, on its low energy side. This structure is assigned with the help of harmonic Franck-Condon factor calculations that use the UCCSD(T)-F12a/VQZ-F12 computed adiabatic ionization energy (AIE), and UCCSD(T)-F12a/VQZ-F12 computed equilibrium geometric parameters and harmonic vibrational frequencies for the H2O2 X̃(1)A state and the H2O2(+) X̃(2)Bg state. These calculations show that the main vibrational structure on the leading edge of the first TPE band is in the O-O stretching mode (ω3) and the HOOH deformation mode (ω4), and comparison of the simulated spectrum to the experimental spectrum gives the first AIE of H2O2 as (10.685 ± 0.005) eV and ω4 = (850 ± 30) and ω3 = (1340 ± 30) cm(-1) in the X̃(2)Bg state of H2O2(+). Contributions from ionization of vibrationally excited levels in the torsion mode have been identified in the TPE spectrum of the first band and the need for a vibrationally resolved TPE spectrum from vibrationally cooled molecules, as well as higher level Franck-Condon factors than performed in this work, is emphasized.

A vibrational spectroscopy study on anserine and its aqueous solutions

In this study based on vibrational spectroscopic measurements and Density Functional Theory (DFT), we aimed for a reliable interpretation of the IR and Raman spectra recorded for anserine in the solid phase and water (H2O) and heavy water (D2O) solutions. Initial DFT calculations at the B3LYP/6-31G(d) searched possible conformers of the anserine zwitterion using a systematic conformational search. The corresponding equilibrium geometrical parameters and vibrational spectral data were determined for each of the stable conformers (in water) by the geometry optimization and hessian calculations performed at the same level of theory using the polarized continuum model (PCM). The same calculations were repeated to determine the most energetically preferred dimer structure for the molecule and the associated geometry, force field and vibrational spectral data. The harmonic force constants obtained from these calculations were scaled by the Scaled Quantum Mechanical Force Field (SQM) method and then used in the calculation of the refined wavenumbers, potential energy distributions, IR and Raman intensities. These refined theoretical data, which confirm the zwitterion structure for anserine in the solid phase or aqueous solvents, revealed the remarkable effects of intermolecular hydrogen bonding on the structural properties and observed IR and Raman spectra of this molecule.

Vibrational spectra and electronic structure of 3-((1H-pyrrol-1-yl) methyl) naphthalen-2-ol – A computational insight on antioxidant active Mannich base

The 3-((1H-pyrrol-1-yl) methyl) naphthalen-2-ol (IFTN) is a class of synthesized organic Mannich base compound having antioxidant property of biological importance. A meticulous normal mode vibrational analysis has been carried out by comparing and contrasting the experimentally recorded FT-IR and FT-Raman spectra with simulated spectra of IFTN. Similarly the calculated 1H and 13C NMR of IFTN were correlated with experimental findings to understand the shielding and deshielding nature hold in it. The following other electronic structure properties were calculated such as equilibrium geometrical parameters, natural bond orbital analysis (NBO), frontier molecular orbital (FMO) characterization, statistical thermochemical properties against a range of temperatures and molecular electrostatic potential (MEP) imprint was carried out along with various charges such as APT, ESP, Hirshfeld, natural and Mulliken. All these predicted properties unlock the nature of total behavior of IFTN in various dimensions. These could be Lewis, non-Lewis interaction along with their respective energies, contribution of fragmented moieties for various orders of HOMO and LUMO, temperature consequences on enthalpy, entropy, and heat capacity. In addition, the MEP leads to find electrophilic, nucleophilic reactive sites on IFTN molecular surface. The entire computational calculations has been made on HF/6-31+G/6-311++G(d,p) and B3LYP/6-31+G/6-311++G(d,p) model chemistries. A complete electronic structure observation has been achieved by this theoretical analysis.

Experimental and theoretical study on free 5-nitroquinoline, 5-nitroisoquinoline, and their zinc(II) halide complexes

In this study where the interpretations of the experimental IR and Raman spectra recorded at room temperature for the ligands 5-nitroquinoline (5NQ) and 5-nitroisoquinoline (5NIQ) and also for their Zn(II) halide (halogen: chlorine, bromine, iodine) complexes were first reported, the assignments of the observed fundamental bands were achieved in the light of the vibrational spectral data and total energy distribution (TED) values calculated at B3LYP/6–311++G(d,p) and B3LYP/LANL2DZ levels of theory. The equilibrium geometrical parameters, Natural Bond Orbital (NBO) charges and frontier orbital (HOMO, LUMO) energies of these molecular structures were also calculated at the same level of theory. Comparisons over the corresponding experimental and theoretical data obtained for the title ligands and their complexes revealed that in complex form both ligands bond to Zn(II) ion through their ring nitrogen atoms and NO2 groups at the same time.

Molecular structure, vibrational spectra (FTIR and FT Raman) and natural bond orbital analysis of 4-Aminomethylpiperidine: DFT study

The FT-IR and FT-Raman spectra of 4-Aminomethylpiperidine have been recorded using Perkin Elmer Spectrophotometer and Nexus 670 spectrophotometer. The equilibrium geometrical parameters, various bonding features, the vibrational wavenumbers, the infrared intensities and the Raman scattering activities were calculated using Hartree–Fock and density functional method (B3LYP) with 6-311+G(d,p) basis set. Detailed interpretations of the vibrational spectra have been carried out with the aid of the normal coordinate analysis. The spectroscopic and natural bonds orbital (NBO) analysis confirms the occurrence of intra molecular hydrogen bonds, electron delocalization and steric effects. The changes in electron density in the global minimum and in the energy of hyperconjugative interactions of 4-Aminomethylpiperidine (4AMP) were calculated. The theoretical UV–Visible spectrum of the compound was computed in the region 200–400nm by time-dependent TD-DFT approach. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. The dipole moment (μ) and polarizability (α), anisotropy polarizability (Δα) and hyperpolarizability (β) of the molecule have been reported.

Electron diffraction study of the equilibrium structure of hexamethylenetetramine involving data from quantum chemistry and vibrational spectroscopy

The equilibrium structure of the urotropine molecule is characterized by means of gas electron diffraction (GED) with the involvement of quantum chemistry and vibrational spectroscopy. A structural analysis of the GED data is performed based on the parameters of the intramolecular potential function using of the program complex SYMM/DISP/ELDIFF/LARGE. The quadratic and cubic force constants of the urotropine molecule were obtained earlier on the basis of calculations at the MP2(full)/cc-pVTZ level and assuming molecular symmetry Td. The values of the equilibrium geometric parameters re of the urotropine molecule are found. The experimental structural parameters are in good agreement with those calculated at the MP2(full)/cc-pVTZ level.

Theoretical study of the structure and stability of oxo heme derivatives

The geometric and electronic structures, energy stability, and normal mode frequencies of molecules and ions of oxo heme derivatives Heme=O0,±, Heme-O-Heme0,±, Heme-OO0,±, and Heme-OO-Heme0,± (Heme=FeC34H32N4O4) in the states of different multiplicity have been calculated by the density functional theory B3LYP method with several basis sets. Energetically preferred states have been determined, and the energies of different channels of their decomposition with dissociation of the Fe-O and O-O bonds have been estimated. The relative energies of superoxide and peroxide isomers of the dioxygenyl complexes Heme-OO0,± and Heme-OO-Heme0,± have been estimated. For the double-decker Heme-OO-Heme0,± complexes, local minima (intermediates) have been found, which correspond to the structures containing rhombic Fe(μ-O)2Fe moieties with the iron atoms linked by two covalent oxygen bridges Fe-O-Fe. The trends in the behavior of the equilibrium geometric parameters, vibrational frequencies, and spin density distribution between the Fe and O atoms and the porphyrin ring of oxohemes have been analyzed as a function of the electronic state multiplicity and the external charge of the complex.

Ab initio study of scandium fluoride molecules: ScF, ScF2, AND ScF3

Equilibrium geometric parameters, normal mode frequencies and intensities in IR spectra, atomization enthalpy, and relative energies of low-lying electronic states of scandium fluoride molecules (ScF, ScF2, and ScF3) are calculated by the coupled-cluster method (CCSD(T)) in triple-, quadruple, and quintuple-zeta basis sets with the subsequent extrapolation of the calculation results to the complete basis set limit. The ScF molecule is also studied by the CCSDT technique. The error in the approximate calculation of triple excitations in the CCSD(T) method does not exceed 0.002 A for the equilibrium internuclear distance Re, 4 cm−1 for the vibrational frequency, and 0.2 kcal/mol for the dissociation energy of the molecule. In the ground electronic state \(\tilde X^2 \)A1(C2ν) of ScF2 molecules, Re(Sc-F) = 1.827 A and αe(F-Sc-F) = 124.2°; the energy barrier to bending (linearization) h = Emin(Dg8h) − Emin(C2ν) = 1652 cm−1. The relative energies of A2Δg and \(\tilde B^2 \)Πg electronic states are 3522 cm−1 and 14633 cm−1 respectively. The bond distance in the ScF3 molecule (\(\tilde X^1 \)A′1, D3h) is refined: Re(Sc-F) = 1.842 A. The atomization enthalpies ΔatH2980 of ScFk molecules are 139.9 kcal/mol, 289.0 kcal/mol, and 444.8 kcal/mol for k = 1, 2, 3 respectively.

Stabilizing hydrogen-hydrogen interactions in cationic indopolycarbocyanine dyes

A quantum chemical DFT method with the hybrid B3LYP functional in the 6-31G(d) basis set is employed to calculate the equilibrium geometric parameters of the ground and excited states of cationic symmetric indopolycarbocyanine dyes. Based on the Bader topological analysis of the electron density distribution function, it is found that there are hydrogen-hydrogen bonding interactions in the ground, first singlet, and first triplet states of the studied compounds. These interactions are assumed to have the dispersion character. The effect of the stabilization of the conformational position of methyl groups due to hydrogenhydrogen interatomic interactions on fluorescence deactivation processes is shown. The total stabilization energy of hydrogen-hydrogen interatomic interactions in dye cations is found, which is ≈9 kcal/mol.