DFT Study on Methanofullerene Derivative [6,6]-Phenyl-C61 Butyric Acid Methyl Ester

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) with hybrid functional B3LYP were used to investigate several physical and chemical properties of [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM), including the geometry, electron structure, charge population, bond properties, as well as IR, Raman and electronic absorption spectra. The analysis of the natural bond orbital (NBO) suggested that there were about 0.11 electrons transferred from moiety phenyl and butyric acid methyl ester group of PCBM to fullerene cage. The strongest IR and Raman peaks came from different modes with the frequencies of 1773 and 1492 cm⁻¹, respectively. The calculated isotropic polarizability, polarizability anisotropy invariant, and hyperpolarizability were 577.7, 96.9, and −22.8 a.u., respectively. Based on TDDFT, the electronic absorption spectra of PCBM were calculated and analyzed. The calculated absorption band near 349 nm agreed well with the experimental measurement.     

Theoretical study of vibration spectra of sensitizing dyes for photoelectrical converters based on ruthenium(II) and iridium(III) complexes

Quantum-chemical method of the density functional theory was employed to calculate, with the use of a B3LYP hybrid exchange-correlation functional, the IR absorption and Raman spectra of [Ru(bpy)₂(CN)₂] and [Ir(bpy)₂(CN)₂]⁺ complexes. All the normal vibrational frequencies were analyzed and new assignments of a number of bands in the IR absorption and Raman spectra were made. The role of vibrational motions of metal atoms and ligands in the vibronic deformation of electron shells in the course of electron transfer was discussed. This was done using data on surface-enhanced Raman spectra of [Fe(bpy)₂(CN)₂] and [Ru(bpy)₃]²⁺ complexes adsorbed on the surface of colloid silver.     

On the geometry and internal rotation of XSCF3 compounds (X = F,Cl and CF3)

The molecular structures (r_α⁰ values) for XSCF₃ with X = F, Cl and CF₃ have been determined by electron diffraction of gases. While the geometry (C-F bond length and FCF angle) of the CF₃ groups and the bond angle at the sulfur atom depend very little on the substituent X, the S-C bond length increases with decreasing electronegativity of X from 1.805 (3) Å for X = F to 1.824 (6) Å for X = Cl. Torsional force constants for the CF₃ groups were derived from vibrational amplitudes. A strong increase of this force constant is observed between FSCF₃ (f_τ = 0.09 (2) mdyn Å) and CISCF₃ (f_τ = 0.18 (5) mdyn Å). The torsional frequencies derived from the electron diffraction experiment agree very well with the values observed in the far IR spectra for CISCF₃, and CF₃SCF₃. A force field for CF₃SCF₃ has been derived from IR and Raman data.     

The Fermi doublet V2−V3 + V4 of CH3CN as a probe of molecular interactions

The Fermi doublet V₂?V₃ + V₄ of CH₃CN in basic, inert and acidic solvents has been studied by IR and Raman spectroscopy. The values of W, the Fermi coupling coefficient, obtained from IR spectra varies with the nature of the solvent while W evaluated from Raman data remains constant at 12.5 ± 0.5 cm^?1. The similar effects of Bronsted and Lewis acids on the band frequencies and intensities is evidence that the CN group complexes with acids via the N atom “n” electron pair and not the π bond.     

Vibrational spectra and noncovalent interactions of carbohydrates molecules

The differences between the vibrational spectra of carbohydrates of the same chemical structure caused by the noncovalent intra- and intermolecular interactions have been systematized. In the general case, these differences show up as the following specific features of changes in the bond intensities: change in the intensity ratio of closely spaced bands (IR and Raman spectra); selective change (increase, decrease) in intensities of individual bands (IR and Raman spectra); change (increase, decrease) in intensities of practically all bands (IR and Raman spectra); appearance of strong bands in the region of low frequencies from 50 to 200 cm⁻¹ (Raman spectra); appearance of strong diffuse bands in the low-frequency range with a simultaneous great reduction in the other bands (practical disappearance of the majority of bands) (Raman Spectra). The causes of such a kind of changes in the band intensities in the vibrational spectra of carbohydrates are discussed.     

Structural and spectroscopic study of chelate carbonyl and phosphoryl antimony(v) complexes

Chelate complexes of antimony tetrachloride with dibenzoylmethane and (benzoylchloro-methyl)diphenylphosphine oxide were stndicd by X-ray diffraction, I R, and Raman spectroscopy. The antimony atom has a slightly distorted octahedral coordination in the complexes. The bond lengths in the chelate cycles are evidence for an appreciable electron delocalization in the O-C-C-C-0 and O-C-C-P-0 chains. Unlike the C₃O₂Sb chelate cycle, the chelate cycle with the phosphorus atom is nonplanar. The assignment of the stretching vibrations frequencies of the C-O, P-0, C-C, Sb-O, and Sb-CI bonds was presumably made on the basis of the IR and Raman spectral data.Deceased in 1995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1474–1479, June, 1996.     

IR and Raman spectroscopic study of the photopolymerization of Langmuir-Blodgett films of acetylenic acids

The UV induced photopolymerization of Langmuir-Blodgett films of lead salt of 2-docosynoic acid (CH₃(CH₂)₁₈C=CCOOH) is studied using IR and Raman spectroscopy. It is found that the films are a highly ordered system with trans-configuration of alkyl chains and a bridged complex generated between the carboxyl group and the lead ion. Based on a change in the absorption band intensity in the IR spectra corresponding to the triple bond vibration, the degree of polymerization depending on the irradiation time is determined. In the Raman spectra, a peak at ∼1635 cm⁻¹ appears during polymerization, which corresponds to the C=C double bond. The formation of conjugated double bonds in these systems is observed for the first time. During polymerization, methylene chains of molecules retain trans-configuration; the structural ordering of molecules in the film is observed.     

Structural features of disubstituted polyacetylenes with bulky substituents at double bonds

The structural features of polyacetylenes carrying two substituents at double bonds with the general formula [-C(CH₃)=CR-] _n , where R = Si(CH₃)₃, -Ge(CH₃)₃, or CH(CH₃)₂, are studied. It is shown that the experimental IR and Raman spectra of the polymers and the theoretically calculated vibrational spectra for the model polymers consisting of three units coincide well with experimental data. All bands in the IR spectra are interpreted. The potential curves of internal rotation are calculated and constructed; high values of rotation barriers indicate a high rigidity of chains for all polymers of interest. The orthogonal arrangement of neighboring monomer units and, as a result, the absence of electron-density conjugation over the polymer chain are revealed. Charges on atoms and electron density on bonds of the monomer unit obtained from theoretical calculations indicate the presence of strong polarization of all bonds, including the -C=C- bond. This effect causes a shift in the frequencies of stretching vibrations due to double bonds in the IR spectra of polyacetylenes with Si- and Ge-containing side substituents toward the longwave region. For polyacetylene with hydrocarbon side substituents -CH(CH₃)₂, such polarization is absent.     

The infrared,Raman and mass spectra of F3C-CC-CC-CF3

The IR spectra of the vapor, liquid and solid phases of hexafluorohexa-2-diyne, F₃C-CC-CC-CF₃, were measured. The liquid phase Raman spectrum with polarizations was measured. These vibrational spectra fit D_3d selection rules, establishing that the molecule has a linear carbon skeleton. The IR spectra indicate that the -CF₃ groups rotate freely in the vapor phase, but that conformers exist in the condensed phases. The electron impact mass spectrum was measured and the molecular ion produced the strongest peak.     

Vibrational spectra and reinvestigation of the crystal structure of a polymeric copper(II)-orotate complex, [Cu(μ-HOr)(H2O)2]n: The performance of new DFT methods, M06 and M05-2X, in theoretical studies

The crystal and molecular structure of a polymeric Cu(II)-orotate complex, [Cu(μ-HOr)(H₂O)₂]_n, has been reinvestigated by single crystal X-ray diffraction. It is shown that several synergistic interactions: two axial Cu-O interactions; intramolecular and intermolecular hydrogen bonds; and π-π stacking between the uracil rings contribute to the stability of the crystal structure. The Raman and FT-IR spectra of the title complex are reported for the first time. Comprehensive theoretical studies have been performed by using three unrestricted DFT methods: B3LYP; and the recently developed M06, and M05-2X density functionals. Clear-cut assignments of all the bands in the vibrational spectra have been made on the basis of the calculated potential energy distribution, PED. The very strong Raman band at 1219 cm⁻¹ is diagnostic for the N1-deprotonation of the uracil ring and formation of the copper-nitrogen bond, in this complex. The Cu-O (carboxylate) stretching vibration is observed at 287 cm⁻¹ in the IR spectrum, while the Cu-N (U ring) stretching vibration is assigned to the strong Raman band at 263 cm⁻¹. The molecular structure and vibrational spectra (frequencies and intensities) calculated by the M06 functional method are very similar to the results obtained by the B3LYP method, but M06 performs better than B3LYP in calculations of the geometrical parameters and vibrational frequencies of the interligand O-H?O hydrogen bonding. Unfortunately, the M05-2X method seriously overestimates the strength of interligand hydrogen bond.     

Conformational properties of methyl vinyl sulfone: Ab initio geometry optimization and vibrational analysis

An ab initio conformational analysis of methyl vinyl sulfone (CH₂CHSO₂CH₃) has been carried out. Molecular geometry optimizations have been performed at the HF and MP2 levels of the theory. Relative energies of the stationary points have been determined by using different approaches, including electron correlation corrections up to the third order. The IR and Raman spectra of the liquid have been measured and a vibrational assignment is proposed. The height of the barrier to the methyl group internal rotation has been estimated. Theoretical calculations and vibrational spectra have shown that the predominant conformation of methyl vinyl sulfone has the C=C bond eclipsed with one of the S=O bonds. Similar eclipsed forms have been found in vinyl fluoro sulfone, vinyl chloro sulfone and divinyl sulfone by ab initio HF calculations.     

Darstellung und eigenschaften von heterocyclischen silanen des typs Si4X MIT X = B,N, O

Five-membered heterocycles Si₄Ph₈X with X = BNMe₂, NMe, NEt and O were prepared and characterised with ¹H NMR, UV, far IR and Raman spectra. The problem of electron delocalisation in these ring systems containing an electron excess (N) or an electron deficit (B), respectively, is discussed. These measurements suggest that there is no delocalisation.     

Simulation of the Raman spectra of zwitterionic glycine + nH2O (n = 1, 2, …, 5) by means of DFT calculations and comparison to the experimentally observed Raman spectra of glycine in aqueous medium

Raman spectra of an aqueous solution of glycine (Gly) have been recorded in the range of 400-2000 cm⁻¹. In aqueous solution, glycine molecules exist in their zwitterionic form, having two opposite charged poles, COO⁻ and NH₃⁺. The zwitterionic structure of glycine (ZGly) is stabilized by the hydrogen bond interaction of water (W) molecules. In the present report, we have optimized the ground state geometries of different hydrogen bonded complexes of [ZGly + (W)_n=1-5] in aqueous medium using DFT calculations at the B3LYP/6-311++G(d) level of theory. A comparative discussion on the structural details and binding energies (BEs) of each conformer has been also done. The theoretical Raman spectra were calculated corresponding to the most stable [ZGly + (W)_n=1-5] conformers. The theoretically simulated Raman spectra of each stable conformer were compared with experimentally observed Raman spectra to explore the number of water molecules needed for stabilizing the structure of ZGly. The theoretically simulated Raman spectra corresponding to the most stable conformer of [ZGly + (W)₅] having a BE of −22.8 kcal/mol, are matching nicely with the experimentally observed Raman spectra. Thus, on the basis of the above observations, we conclude that the conformer, [ZGly + (W)₅] is the most probable conformer in the aqueous medium. We also believe that in the conformer, [ZGly + (W)₅] the five water molecules are arranged around the ZGly in such a way that the effect of steric hindrance is less compared to the other conformers. The dipole-dipole interaction potential (DDP) is also calculated corresponding to the strongest hydrogen bond for each [ZGly + (W)_n=1-5] conformer.     

Vibrational spectra of a ferrocenyl phosphine derivative chemisorbed on 3-aminopropylsilyl modified silica gel

Samples of silica gel dried at different temperatures, silica gel modified with 3-aminopropylsilyl (APS) and silica gel modified with APS and further with a ferrocenyl phosphine derivative were investigated by DRIFT, transmission FTIR and MicroRaman spectroscopy. The reaction between 3-aminopropyltrimethoxysilane (APTMS) and silica gel was mainly identified by the diminishing or vanishing intensity of the stretching band of the free OH groups in the silica gel. Further chemical reaction of the APS groups with a ferrocenyl phosphine derivative (suitable as ligand in homogeneous catalysis) was identified in the IR spectra by the appearance of the CN stretching band of the formed Schiff base, and diminishing intensity of the δ(NH₂) modes. According to the IR spectra the reaction of the ferrocenyl phosphine derivative with the APS-modified silica gel is almost quantitative. From the recorded IR and Raman spectra, conclusions concerning the substitution of APTMS methoxy groups during the chemisorption on silica gel were derived. Through deconvolution of the complex Raman band in the siloxy stretching region of the APS-modified silica gel, the newly formed siloxy bond was identified.     

Electrical Conductivity and Physical Properties of Poly(Dipropargylsilane Derivatives) Doped with Electron Acceptors

Abstract

Films of poly(dipropargylsilane derivatives) were easily prepared by solvent casting. The resulting red-black films were relatively flexible and ductile. By doping with electron acceptors, the electrical conductivity increased up to the order of 10^?1-10⁰ S/cm. The activation energy for the conduction of doped film was 4 kcal/mol. The change in Raman, IR, and UV-visible spectra by doping suggests electron transfer from the poly(dipropargylsilane derivatives) to the dopant, leading to the formation of polaron. It also was observed that doping with I₂ drastically destroys the crystallinity of the polymer.     

Infrared and Raman multi-phonon spectra and structure of PbWO4

Improved Raman spectra of PbWO₄ show previously reported spectra contain large polarization and/or orientation errors. New spectroscopic information, obtained from polarized IR reflection and Raman spectra, allowed us to assign the IR and the previously unreported Raman multi-phonon bands. It was also used to show that it determines uniquely the C_4h factor group of PbWO₄. The use of IR reflection vs. infrared transmission spectra in the vibrational determination of crystal structures is also discussed.     

The vibrational spectra, molecular structure and conformation of organic azides Part III. 2,3-Diazido-1,3-butadiene

A sample of 2,3-diazido-1,3-butadiene has been synthesized from 1,4-dibromo-2-butyne and tetramethylguanidinium azide. The highly explosive sample has been studied by gaseous electron diffraction and by IR spectroscopy. Only incomplete Raman spectra have been recorded due to sample decomposition in the laser beam. The title compound is found to be planar with the CNN angle equal to 114.5°, oriented syn to the adjacent C=C double bond; the NNN angle is ca. 167°, oriented anti to the C---N bond. The following bond distances (r_a) are obtained: N---N(N), 114.1; N---N(C), 124.2; C---N, 143.2; C=C 134.8; and C---C, 148.5 pm. The vibrational spectra are tentatively assigned in terms of C_2h molecular symmetry, supported by force constant calculations.     

Gamma ray induced changes on vibrational spectroscopic properties of strontium alumino-borosilicate glasses

The present investigation reports the effect of influence of aluminum ions on radiation damage of strontium borosilicate glasses studied by means of spectroscopic (viz., optical absorption (OA), infrared and Raman spectra). The composition of the glasses chosen for the study is 40SrO–xAl₂O₃–(15-x) B₂O₃–40SiO₂ (x = 5, 7.5, 10), all in mol%. The glasses were synthesized by conventional melt quenching method. Later, the samples were exposed to gamma (γ) radiation dose of strengths 10 kGy and 30 kGy with a dose rate of 1.5 Gy/s using ⁶⁰Co as radiation source. The infrared spectra (IR), Raman spectra and optical absorption (OA) spectra of the samples were recorded at ambient temperature before and after irradiation. The OA spectra of the pre-irradiated samples do not exhibit any absorption bands in the UV–vis regions and IR and Raman spectra exhibited conventional vibrational bands due to different borate, silicate AlO₄ and AlO₆ structural units. The OA spectra of post irradiated samples exhibited a broad absorption band in the wavelength region 600–750 nm; it is attributed to electron trapped color centers. The intensity of this peak is observed to increase with increase of the γ-ray dose. Considerable changes in the intensities of various bands in the IR and Raman spectra were also observed. The changes were explained based on structural modifications taking place in the glass network due to γ-ray irradiation and finally it is concluded that the glasses mixed with 10.0 mol% of Al₂O₃ are relatively more radiation resistant.     

Density functional theory studies on covalent functionalization of single-walled carbon nanotubes with benzenesulfonic acid

The calculated Raman spectra of the covalently functionalized zigzag single-walled carbon nanotubes, f-(n,0)-SWCNTs (n = 6–10), with benzenesulfonic acid showed that the radial breathing modes (RBMs) frequencies (ω_RBM) of the sidewall functionalized tubes are red shifted in comparison with the frequencies of their non-functionalized counterparts, (n,0)-SWCNTs. It is also observed that this ω_RBM red-shift is tube-diameter (d_t) dependent, where almost no redshifts are observed for the (10,0)-SWCNT. Moreover, many new Raman bands, which results from the functional group, appear in the low energy region, ranging from 100 to 600 cm⁻¹. In the high frequency region, resulting from the functional group, the Raman spectra of the f-(n,0)-SWCNTs exhibited a few new peaks above the tangential bands of the SWCNTs (ranging from 1580 to 1650 cm⁻¹), which entirely belongs to the CC stretching, including bending deformation of the CCC bonds, and rock of CH in phenyl group of the benzenesulfonic acid as well as many new Raman peaks dispersed through spectrum. The calculated IR spectra also exhibited many new peaks through spectra of the f-(n,0)-SWCNT when comparing these with corresponding IR spectrum of the isolated nanotube. Furthermore, the calculated vertical singlet-singlet electronic transitions of the f-(n,0)-SWCNTs significantly altered in the optical structure of the nanotube and exhibited charge transfer states for both the functionalized (8,0)- and (12,0)-SWCNTs. The small distances among the calculated dipole-allowed and forbidden electronic energy levels also suggested an internal crossing (IC) processes.     

Vibrational spectra and electron diffraction study of the structure and internal rotation of N,N-diethylcyanamide

Structural parameters, internal rotation parameters, and frequencies of normal vibrations of N,N-diethyl-cyanamide were obtained. The geometrical structure and internal rotation were studied by gas phase electron diffractometry. The configuration of the bonds of the amine nitrogen atom were found to be close to pyramidal: λ∈CNC 111.8°, λCNC 109.1°; the main bond lengths are (Å): N∈C 1.174; ∈C?N 1.349; C?N 1.479; C?C 1.536. A map of changes in the conformation energies due to rotation of ethyl groups around the N?C bonds is constructed. Experimental IR and Raman spectra of pure liquid and CCl₄ solution were measured. The frequencies and forms of normal vibrations are calculated, and the force constants are determined.