Crystal and molecular structure of 2‐amino‐5‐chloropyridinium hydrogen selenate—its IR and Raman spectra,DFT calculations and physicochemical properties

The new organic‐inorganic salt, 2‐amino‐5‐chloropyridinium hydrogen selenate, has been synthesised and characterised by means of FT‐IR, FT‐Raman and single crystal X‐ray crystallography. Its vibrational spectra have been discussed on the basis of quantum chemical DFT calculations using the B3LYP/6‐31G(d,p) approach. The crystal and molecular structures have been compared and the role of the intermolecular interactions in this crystal has been analysed. The N HO interactions between the hydrogen atoms of the organic cation and oxygen atoms of hydrogen selenate anion determine the supramolecular arrangement in three‐dimensional space. The possible application of the studied composite material as a Raman laser has been discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Electron–phonon coupling and vibrational modes contributing to linear electro‐optic effect of the efficient NLO chromophore 4‐(N,N‐dimethylamino)‐N‐methyl‐4′‐toluene sulfonate (DAST) from their vibrational spectra

The optimized geometry and structural features of the most prospective electro‐optic crystal 4‐(N,N‐dimethylamino)‐N‐methyl‐4′‐toluene sulfonate (DAST), and the vibrational spectral investigations have been comprehensively described with the near infrared Fourier transform (NIR FT) Raman and Fourier transform infrared (FT‐IR) spectra supported by the density functional theoretical (DFT) computations to elucidate the contribution of vibrational modes to the linear electro‐optic (LEO) effect. Mulliken population analysis and natural bond orbital (NBO) analysis have also been carried out to analyze the effects of intramolecular charge transfer (ICT), intramolecular hydrogen bonding and hyperconjugative interactions on the geometries. The influence of CT interaction between the phenyl ring and the dimethylamino group of the nonlinear optical (NLO) chromophore on the endocyclic and exocyclic angles, and the electronic effects such as hyperconjugation and back‐donation on the methyl hydrogen atoms have been examined. The concurrent intense activation of Raman and IR activities of the effective conjugation vibrational coordinate, which significantly contributes to the LEO effect resulting from the strong electron–phonon (e/ph) coupling, has been analyzed in detail. The effects of frontier orbitals, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), transition of electron density (ED) transfer and the influence of planarity in the stilbazolium ring on the first hyperpolarizability are also discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational spectral studies on charge transfer and ionic hydrogen‐bonding interactions of nonlinear optical material L‐arginine nitrate hemihydrate

The near infrared Fourier‐transform (NIR FT)‐Raman and Fourier‐transform infrared (FT‐IR) spectroscopies supported by HF/6‐31G(d) computations have been employed to derive equilibrium geometry, vibrational wavenumbers and the first hyperpolarizability of the nonlinear optical (NLO) material, L ‐arginine nitrate (LAN) hemihydrate. The reasonable NLO efficiency, predicted for the first time in this novel compound, has been confirmed by Kurtz–Perry powder second harmonic generation (SHG) experiments. The changes in the atomic charge distribution among different groups due to the presence of strong electronegative atoms and the shrinking of N O bonds of nitrate anion and C N bonds of guanidyl group have been analyzed. The splitting of the carboxylate stretching modes, blue shifting of methine vibrations and the electronic effects such as backdonation and induction on the methylene hydrogen atoms have also been examined in detail. The intense low wavenumber H‐bond Raman vibrations due to electron–phonon coupling and nonbonded interactions in making the LAN molecule NLO active have been discussed based on the vibrational spectral features. The natural bond orbital (NBO) analysis and HF computations confirm the occurrence of strong intra‐ and intermolecular N H·O and O H·O ionic hydrogen bonding between charged species providing the noncentrosymmetric structure in the LAN crystal. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectroscopic,structural and theoretical studies of 2‐methyl‐4‐nitroaniline (MNA) crystal. Electronic transitions in IR

Polarized FT‐IR, Raman, neutron scattering (IINS), and UV‐Vis‐NIR spectra of 2‐methyl‐4‐nitroaniline (MNA) crystal plates, powder, and solutions were measured in the 10–50 000 cm⁻¹ range. The FT‐IR spectrum of deuterated MNA (DMNA) in KBr pellet, the Raman spectrum of the DMNA powder as well as the EPR spectrum of the MNA powder were also recorded. Complete assignments of bands to normal vibrations have been proposed. Density functional theory (DFT) calculations of wavenumbers and potential energy distribution (PED) have been performed to strengthen the assignments. The analysis of vibrational and electronic spectra has revealed vibronic couplings in MNA molecules in solutions and in crystals. In the polarized FT‐IR spectra of the crystal five unusually large bands are observed in MIR and NIR regions. Their origin is discussed in terms of N H···O, C H···O, C H···H N hydrogen bonds, intermolecular charge transfers, electrostatic interactions, and ion radicals formation in the crystal. The role of a methyl group introduction to 4‐nitroaniline is analyzed. The crystal structure of MNA at the room temperature was re‐investigated. Copyright © 2008 John Wiley & Sons, Ltd.     

The revision of intermolecular interactions in 1,3‐dinitrobenzene crystal—the role of nitro groups in optical nonlinearity

Polarized Fourier transform‐infrared (FT‐IR) reflectance spectra and powder Raman spectra have been measured for 1,3‐dinitrobenzene crystal in order to revise the assignments of bands by means of the oriented gas model reinforced with quantum chemical [density functional theory (DFT)] calculations. Longitudinal optical/transverse optical (LO‐TO) splitting of some bands is observed indicating medium strong, long‐range, dipole–dipole interactions. The analysis of overtones in the polarized FT‐NIR spectra has allowed us to estimate the anharmonicity of vibrations in the crystal. The molecular motions of the nitro groups are analyzed on the basis of temperature‐dependent polycrystalline IR spectra. Based on the values of the energy difference (Δν_el) between the forbidden A_1g→B_2u transition in the benzene molecule in the gas phase and the first electronic transition in 1,3‐dinitrobenzene, it has been concluded that the intermolecular interactions are medium strong. The nitro group interactions are proposed to play the main role in the optical nonlinearity. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and Raman spectroscopic investigation of a new self‐assembly monolayer material 4‐[N‐phenyl‐N‐(3‐methylphenyl)‐amino]‐benzoic acid for organic light‐emitting devices

We have synthesized 4‐[N‐phenyl‐N‐(3‐methylphenyl)‐amino]‐benzoic acid (4‐[PBA]) and investigated its molecular vibrations by infrared and Raman spectroscopies as well as by calculations based on the density functional theory (DFT) approach. The Fourier transform (FT) Raman, dispersive Raman and FT‐IR spectra of 4‐[PBA] were recorded in the solid phase. We analyzed the optimized geometric structure and energies of 4‐[PBA] in the ground state. Stability of the molecule arising from hyperconjugative interactions and charge delocalization was studied using natural bond orbital analysis. The results show that change in electron density in the σ* and π* antibonding orbitals and E₂ energies confirm the occurrence of intramolecular charge transfer within the molecule. Theoretical calculations were performed at the DFT level using the Gaussian 09 program. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution. The good agreement between the experimental and theoretical spectra allowed positive assignment of the observed vibrational absorption bands. Finally, the calculation results were applied to simulate the Raman and IR spectra of the title compound, which show agreement with the observed spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and structural study of 2′‐ and 2′,6′‐positioned methyl‐ and nitro‐substituted 3‐(arylhydrazono)pentane‐2,4‐diones

A systematic series of ortho‐methyl‐ and nitro‐substituted arylhydrazones 2–6 formed by Japp–Klingemann reaction between pentane‐2,4‐dione and the respective aryldiazonium salts have been synthesized and studied by X‐ray crystal structure analysis, with added quantum chemical calculations. The optimized molecular geometries based on DFT calculations, enabling determination of relevant rotational barriers, and the calculated bond and ring critical points, using the method of ‘atoms in molecules’, were found to correspond with the experimental data, involving specific molecular conformations and hydrogen‐bonded ring structure dependent on the ortho‐substitution, thus making possible reliable structural prediction of this compound class. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental and theoretical FT‐IR and FT‐Raman spectroscopic analysis of N1‐methyl‐2‐chloroaniline

In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C₇H₈NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. ¹³C and ¹H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies and DFT calculations of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red‐shift of the NH‐stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO‐stretching mode gives the charge transfer interaction through a π‐conjugated path. Copyright © 2008 John Wiley & Sons, Ltd.     

FT‐Raman,FT‐IR spectral and DFT studies on 6, 8‐dichloroflavone and 6, 8‐dibromoflavone

In this study, experimental and theoretical vibrational spectral results of the molecular structures of 6,8‐dichloroflavone (6,8‐dcf) and 6,8‐dibromoflavone (6,8‐dbf) are presented. The FT‐IR and FT‐Raman spectra of the compounds have been recorded together between 4000 and 400 cm⁻¹ and 3500–5 cm⁻¹ regions, respectively. The molecular geometry and vibrational wavenumbers of 6,8‐dcf and 6,8‐dbf in their ground state have been calculated by using DFT/B3LYP functional, with 6‐31 + + G(d,p) basis set used in calculations. All calculations were performed with Gaussian03 software. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Scale factors have been used in order to compare how the calculated and experimental data are in agreement. Theoretical infrared intensities are also reported. Copyright © 2009 John Wiley & Sons, Ltd.     

FT‐IR and FT‐Raman investigations of the chemosensing material para‐hexafluoroisopropanol aniline

As an important chemosensing material involving hexafluoroisopropanol (HFIP) for detecting nerve agents, para‐HFIP aniline (p‐HFIPA) has been firstly synthesized through a new reaction approach and then characterized by nuclear magnetic resonance and mass spectrometry experiments. Fourier transform infrared absorption spectroscopy (FT‐IR) and FT‐Raman spectra of p‐HFIPA have been obtained in the regions of 4000–500 and 4000–200 cm⁻¹, respectively. Detailed identifications of its fundamental vibrational bands have been given for the first time. Moreover, p‐HFIPA has been optimized and vibrational wavenumber analysis can be subsequently performed via density functional theory (DFT) approach in order to assist these identifications in the experimental FT‐IR and FT‐Raman spectra. The present experimental FT‐IR and FT‐Raman spectra of p‐HFIPA are in good agreement with theoretical FT‐IR and FT‐Raman spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Resonance Raman intensity analysisof the excited‐state photochemical dynamicsof dimethyl 1,3‐dithiole‐2‐thione‐4,5‐dicarboxylate in the A‐band absorption

Dimethyl 1,3‐dithiole‐2‐thione‐4,5‐dicarboxylate (DDTD) was synthesized and characterized using NMR, Fourier transform (FT)‐Raman, Fourier transform‐infrared (FT‐IR) and UV spectroscopies. Resonance Raman spectra (RRs) were obtained with 341.5, 354.7 and 368.9 nm excitation wavelengths and density functional calculations were carried out to elucidate the π (S C S) →π* (S C S) electronic transitions and the RRs of DDTD in cyclohexane solution. The RRs indicate that the Franck–Condon region photo dynamics have a multidimensional character with motion predominantly along the CS stretch and the C S symmetric stretch modes in the five‐member heterocycle. A preliminary resonance Raman intensity analysis was carried out and the results for DDTD were compared with previously reported results for 1,3‐dithiole‐2‐thione (DTT). Differences and similarities of the spectra in terms of molecular symmetry and electron density are also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman,SERS spectra and computational calculations of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide were recorded and analyzed. A surface‐enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO stretching mode gives the charge transfer interaction through a π‐conjugated path. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface, which affects the orientation and metal molecule interaction. The first hyperpolarizability and predicted infrared intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive subject for future studies of nonlinear optics. Optimized geometrical parameters of the title compound are in agreement with reported structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Density functional theory calculations and vibrational spectra of 2‐bromo‐4‐chloro phenol and 2‐chloro‐4‐nitro phenol

FTIR and FT Raman spectra of 2‐bromo‐4‐chloro phenol (BCP) and 2‐chloro‐4‐nitro phenol (CNP) were recorded in the region 4000–400 and 4000–50 cm⁻¹, respectively. The molecular structure, geometry optimization, and vibrational wavenumbers were investigated. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using the standard B3LYP/6‐31G** method and basis set combination and was scaled using multiple scale factors, which yield good agreement between the observed and calculated wavenumbers. The results of the calculations are applied to simulate the infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular structure,spectroscopic (FTIR,FTIR gas phase,FT‐Raman) first‐order hyperpolarizability and HOMO–LUMO analysis of 4‐methoxy‐2‐methyl benzoic acid

Vibrational spectral analysis was carried out for 4‐methoxy‐2‐methyl benzoic acid (4M2MBA) by using Fourier transform infrared (FT‐IR) (solid, gas phase) and FT‐Raman spectroscopy in the range of 400–4000 and 10–3500 cm⁻¹ respectively. The effects of molecular association through O H···O hydrogen bonding have been described by the single dimer structure. The theoretical computational density functional theory (DFT) and Hatree‐Fock (HF) method were performed at 6–311++G(d,p) levels to derive the equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities. The scaled theoretical wavenumbers were also shown to be in good agreement with experimental data. The first‐order hyperpolarizability (β₀) of this novel molecular system and related properties (β, α₀ and Δα) of 4M2MBA are calculated using the B3LYP/cc‐pvdz basis set, based on the finite‐field approach. A detailed interpretation of the infrared and Raman spectra of 4M2MBA is reported. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule were also constructed and compared with the experimental one. Copyright © 2010 John Wiley & Sons, Ltd.     

Molecular structure,vibrational spectroscopic,first‐order hyperpolarizability and HOMO,LUMO studies of 3‐hydroxy‐2‐naphthoic acid hydrazide

The Fourier‐transform infrared spectrum of 3‐hydroxy‐2‐naphthoic acid hydrazide (3H2NAH) was recorded in the region 4000–400 cm⁻¹. The Fourier‐transform Raman spectrum of 3H2NAH was also recorded in the region 3500–10 cm⁻¹. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 3H2NAH were carried out by density functional theory (DFT/B3LYP) method with 6‐31G(d,p) as basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the electric dipole moment (µ) and the first‐order hyperpolarizability (β) of the investigated molecule were computed using ab initio quantum mechanical calculations. The UV spectrum was measured in ethanol solution. The calculation results also show that the 3H2NAH molecule might have microscopic nonlinear optical (NLO) behavior with non‐zero values. A detailed interpretation of the infrared and Raman spectra of 3H2NAH is also reported based on total energy distribution (TED). The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The theoretical FT‐IR and FT‐Raman spectra for the title molecule have also been constructed. Copyright © 2009 John Wiley & Sons, Ltd.     

Excited‐state structural dynamics and vibronic coupling of 1,3‐dithiole‐2‐thione—resonance Raman spectroscopy and density functional theory calculation study

1,3‐Dithiole‐2‐thione (DTT) was synthesized and characterized using NMR, FT‐Raman, FT‐IR, UV spectroscopies. Resonance Raman spectra (RRs) were obtained with 341.5, 354.7 and 368.9 nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the RRs of DTT in cyclohexane solution. The RRs indicate that the Franck‐Condon region photodynamics is predominantly along the CS stretch+ H‐CC‐H scissor υ₄, accompanied by the H‐CC‐H scissor υ₃, S‐C‐S symmetric stretch υ₆, CC stretch υ₂, and overtone of the non‐totally symmetric SC‐S2 out‐of‐plane deformation 2υ₁₁. The excited‐state dynamics and the force constant of CS stretch calculated by the RRs were discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

A joint FTIR,FT‐Raman and scaled quantum mechanical study of 1,3‐dibromo‐2,4,5,6‐tetra‐fluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB)

The liquid phase FTIR and FT‐Raman spectra of 1,3‐dibromo‐2,4,5,6‐tetrafluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB) were recorded in the regions 4000–400 cm⁻¹ and 4000–50 cm⁻¹, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure opti1mization and force field calculations based on the density functional theory using the standard B3LYP/6‐31G* method and basis set combination. The scaled force field reproduced the experimental wavenumbers of the molecule for DTFB and PFB, respectively. The effects of halogen substituents on the structure and vibrational wavenumbers have been investigated. Assignments of fundamental modes were made based on the comparison between calculated and experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectra and crystal structure of the di‐amino acid peptide cyclo(L‐Met‐L‐Met): comparison of experimental data and DFT calculations

Experimental Raman and FT‐IR spectra of solid‐state non‐deuterated and N‐deuterated samples of cyclo(L ‐Met‐L ‐Met) are reported and discussed. The Raman and FT‐IR results show characteristic amide I vibrations (Raman: 1649 cm⁻¹, infrared: 1675 cm⁻¹) for molecules exhibiting a cis amide conformation. A Raman band, assigned to the cis amide II vibrational mode, is observed at ∼1493 cm⁻¹ but no IR band is observed in this region. Cyclo(L ‐Met‐L ‐Met) crystallises in the triclinic space group P1 with one molecule per unit cell. The overall shape of the diketopiperazine (DKP) ring displays a (slightly distorted) boat conformation. The crystal packing employs two strong hydrogen bonds, which traverse the entire crystal via translational repeats. B3‐LYP/cc‐pVDZ calculations of the structure of the molecule predict a boat conformation for the DKP ring, in agreement with the experimentally determined X‐ray structure. Copyright © 2009 John Wiley & Sons, Ltd.     

FT‐Raman spectroscopic spectra on 3‐phenylpropylamine inclusion compounds

Some new Hofmann‐3‐phenylpropylamine‐type clathrates with chemical formulae of M(3‐phenylpropylamine)₂ Ni(CN)₄. 2G (MNi or Co, G = 1,2‐dichlorobenzene or 1,3‐dichlorobenzene) have been prepared and their Fourier transform infrared(FT‐IR; 4000–400 cm⁻¹), far‐infrared (600–100 cm⁻¹) and FT‐Raman (4000–60 cm⁻¹) spectra are reported. The ligand molecule, guest molecules, polymeric sheet and metal‐ligand bands of the clathrates are assigned in detail. The compounds are also characterized by thermal gravimetric analysis (TGA), differential thermal analysis (DTA), elemental analysis and magnetic susceptibility measurements. From the results, the monodentate 3‐phenylpropylamine ligand molecule bonds to the metal atom of |M‐Ni(CN)₄ | _∞ polymeric layers in the trans‐gauche‐gauche (TGG) form, and 1,2‐dichlorobenzene or 1,3‐dichlorobenzene molecules are guested by this structure revealing the inclusion ability of the host complexes. Copyright © 2010 John Wiley & Sons, Ltd.