Effects of dynamical couplings in hydrogen bond systems in the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals

This paper presents the investigation results of the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals measured at 293 and 77 K. Analysis of the results concerned the linear dichroic, H/D isotopic and temperature effects observed in the spectra of the hydrogen and deuterium bond at the frequency ranges of the ν_O–H and the ν_O–D bands, respectively. The main spectral properties of the crystals were interpreted in terms of the “strong-coupling” theory on the basis of the hydrogen bond dimer model. The spectra revealed that the strongest vibrational exciton coupling involved the closely-spaced hydrogen bonds, each belonging to a different chain of associated molecules. The reason for two different crystalline systems, are characterized by almost identical ν_O–H and ν_O–D band shapes, is explained. It was proved that a random distribution of the protons and deuterons took place in the lattices of the isotopically diluted crystals.     

Polarized IR spectra of the hydrogen bond in acetic acid crystals

The paper presents the results of our investigations of the polarized IR spectra of the hydrogen bond in crystals of acetic acid, CH₃COOH, as well as in crystals of three deuterium isotopomers of the compound: CH₃COOD, CD₃COOH and CD₃COOD. The spectra were measured at 283 K and at 77 K by a transmission method using polarized light. Theoretical analysis of the results concerned the linear dichroic effects, together with the H/D isotopic and temperature effects observed in the solid-state IR spectra of the hydrogen and of the deuterium bond at the frequency ranges of the ν_O–H and the ν_O–D bands, respectively. Basic spectral properties of the crystals can be interpreted satisfactorily in terms of one of the quantitative theories of the IR spectra of the hydrogen bond, i.e. the “strong-coupling” theory or the “relaxation” theory when a hydrogen bond dimer model is used. From the spectra obtained it resulted that the strongest exciton coupling involved the closely spaced hydrogen bonds, belonging to different chains of associated acetic acid molecules. These results contradict the former explanation of the spectra within a model, which assumed a strong vibrational exciton coupling between four hydrogen bonds in a unit cell. On analyzing the spectra of isotopically diluted crystalline samples of acetic acid it has been proved that a non-random distribution of the protons and deuterons takes place in the hydrogen bond lattices. This non-conventional isotopic effect is a result of dynamical co-operative interactions involving hydrogen bonds in the system. Simultaneously it has been also found that in an individual hydrogen bonded chain in the crystals, distribution of the hydrogen isotope atoms H and D was fully random. The H/D isotopic “self-organization” mechanism most probably involves a pair of hydrogen bonds from each unit cell where each hydrogen bond belongs to a different chain.     

Effects of strong inter-hydrogen bond dynamical couplings in the polarized IR spectra of adipic acid crystals

This paper presents the results of the re-investigation of polarized IR spectra of adipic acid and of its d₂, d₈ and d₁₀ deuterium derivative crystals. The spectra were measured at 77 K by a transmission method using polarized light for two different crystalline faces. Theoretical analysis concerned linear dichroic effects and H/D isotopic effects observed in the spectra of the hydrogen and deuterium bonds in adipic acid crystals at the frequency ranges of the ν_O–H and the ν_O–D bands. The two-branch fine structure pattern of the ν_O–H and ν_O–D bands and the basic linear dichroic effects characterizing them were ascribed to the vibronic mechanism of vibrational dipole selection rule breaking for IR transitions in centrosymmetric hydrogen bond dimers. It was proved that for isotopically diluted crystalline samples of adipic acid, a non-random distribution of protons and deuterons occurs in the dimers (H/D isotopic “self-organization” effect). This effect results from the dynamical co-operative interactions involving the dimeric hydrogen bonds.     

Investigation of molecule properties from electronic absorption spectra of solid and liquid crystals

Among the achievements of 20th century, there is the origin and violent development of the low-temperature technique and low-temperature spectroscopy of molecular crystals in the polarized light. Many obtained results became possible due to the close cooperation between experiment investigators and theorists. This short review traces the evolution of only one trend in the physics of molecular crystals, namely, the investigation of energetic and spatial structure of molecules from the analysis of electronic spectra of molecular crystals. First, for this purpose the possibilities of using the electronic spectra of molecular crystals at low temperatures benzene derivatives and the electronic spectra of liquid ionic crystals are considered. The results of investigations of the electronic absorption spectra for the new class of liquid crystals, namely, ionic metal-organic smectics are presented. Changes in the structure of doping molecules in the ionic liquid crystals under the influence of the dc electric field are analyzed.     

The source of similarity of the IR spectra of acetic acid in the liquid and solid-state phases

This paper explains the problem of the fair similarity of the ν_O-H band contour shapes in the spectra of liquid and crystal samples of hydrogen-bonded acetic acid, in contrast to the corresponding spectral properties of formic acid. It has been proven that regardless of the relative arrangement of hydrogen bonds in each phase, the hydrogen-bonded dimeric systems decide about the profile of the bands. Moreover, the model dimers of different symmetry, i.e., the C_i or C_2v one of the “side-to-side” type arrangement of moieties, yield nearly identical spectra. Qualitatively similar spectral properties in the ν_O-D band frequency range were found for deuterium-bonded formic and acetic acid isotopologues.     

Theoretical investigation of the molecular, electronic structures and vibrational spectra of a series of first transition metal phthalocyanines

A theoretical investigation of the fully optimized geometries and electronic structures of metallophthalocyanines FePc, CoPc, NiPc, CuPc and ZnPc has been conducted with the density functional theory (DFT) method. A comparison between the different molecules for the geometry, molecular orbital, and atomic charge is made. The simulated order of the sizes of the central hole is FePc>CoPc>NiPcNiPc>CuPc>ZnPc, and the atomic charges of the central metal (M=Fe, Co, Ni, Cu, Zn) ions vary in the same order, FePc>CoPc>NiPcCoPc>FePc>CuPc>ZnPc, and the corresponding peaks predicted at 894, 896, 898, 882 and 871 cm(-1), respectively, also exhibit the same order as above-mentioned. Moreover, the lines of fit through plots of the experimental IR and Ra frequencies versus the calculated ones show very good correlations.     

Effects of electronic correlation on local properties of electronic structure of TiO2 and Ti2O3 crystals: DFT and post‐HF approaches

Calculations of the electronic structure of titanium oxides both in periodic and cluster models are performed using RHF, UHF, and DFT methods. The effect of electronic correlation on local properties of electronic structure (charges, valences, covalences, and bond orders) is discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Theoretical studies on the structures and vibrational spectra of Ni, Pd, and Pt phthalocyanines

Electronic structure calculations and spectroscopic assignments for metallophthalocyanines NiPc, PdPc and PtPc are performed on optimized geometries at B3LYP/LANL2DZ level. The order of the sizes of the central hole is computed to be PdPc > PtPc > NiPc, with the hole size of PdPc close to that of PtPc. The Mulliken charges of the central M vary in the order of PtPc > NiPc > PdPc, and the HOMO-LUMO gaps are in the order of NiPc < PdPc < PtPc, in agreement with the experimental result. The simulated IR spectra for the three derivatives are compared with the experimental absorption spectra, and very good consistency has been obtained. The simulated medium intensity bands associated with the metal-ligand vibrations which appear as singlet bands at 880, 877 and 883 cm⁻¹, respectively, exhibit the order of PtPc > NiPc > PdPc, which is the same order as experiment. Furthermore, the metal-ligand vibrational bands for Raman spectra shift in the order NiPc > PtPc > PdPc. The strongest Raman lines predicted at 1562, 1532 and 1534 cm⁻¹ for NiPc, PdPc and PtPc are very sensitive to the metal ion.     

Effect of 1,1,2,2-tetrachloroethane on IR spectra of HCl complexes withN,N-dimethylformamide and 1-methyl-2-pyrrolidone formed by a strong quasi-symmetric hydrogen bond

The effect of 1,1,2,2-tetrachloroethane (TCE) on the IR spectra of HCl complexes withN,N-dimethylformamide (DMF) and 1-methyl-2-pyrrolidone (N-MP) with strong quasisymmetric hydrogen bonds was studied using Multiple Attenuated Total Reflection (MATR) IR spectroscopy. The addition of TCE does not change the background absorption spectra, but results in a change in the extinction coefficients of some bands of these complexes. The analysis of the spectra shows that the HCl−DMF complexes interact only with one molecule of TCE, and the HCl−N-MP complexes interact with two molecules of TCE. It is shown that the neutral component of the system (TCE) has no effect on the parameters of the strong quasi-symmetric H-bond in the complexes studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 956–960, May, 1997.     

Theoretical study of the νO–H IR spectra for the hydrogen bond dimers from the polarized spectra of glutaric and 1-naphthoic acid crystals: Fermi resonances effects

A full quantum theoretical model is proposed to study the ν_O–H experimental IR line shapes of polarized crystalline glutaric and 1-naphthoic acid dimer crystals at room and liquid nitrogen temperatures. This work is an application of a previous model [M. E-A. Benmalti, D. Chamma, P. Blaise, and O. Henri-Rousseau, J. Mol. Struct. 785 (2006) 27–31] by accounting for Fermi resonances. The approach is dealing with the strong anharmonic coupling, Davydov coupling, multiple Fermi resonances between the first harmonics of some bending modes and the first excited state of the symmetric combination of the two ν_O–H modes and the quantum direct and indirect relaxation.Numerical results show that mixing of all these effects allows to reproduce satisfactorily the main features of the experimental IR line shapes of crystalline hydrogenated and deuterated glutaric and 1-naphthoic acid crystals and are expected to provide efficient of Fermi resonances effects.     

Study of hydrogen bond dynamics in Nylon 6 crystals using IR spectroscopy and molecular dynamics focusing on the differences between α and γ crystal forms

Proton dynamics of hydrogen bonds (HBs) in the α and γ form of Nylon 6 were investigated by Born–Oppenheimer molecular dynamics (BOMD). Our results show differences in the dynamic effects of interchain HB interactions between the α form and the γ form of Nylon 6. Analysis of the time course of the geometrical parameters of HBs along the BOMD simulations has shown that HBs are dynamically favored in the γ form of Nylon. The quantization of the N H stretching mode enables a detailed discussion of the strengths of HB interactions. Solving the Schrödinger equation for the snapshots of one‐dimensional proton potentials, extracted from the ab initio MD, enables the consideration of anharmonicity, thermodynamics, and approximate quantum effects on proton movement. A larger red shift of the N H stretching band was observed in the γ form compared with the α form. Our study shows that HBs are more stabilized in the γ form than in the α form, which is mainly due to the higher number of HBs. The distribution of HBs along the trajectory clearly reveals the preference of the γ form. The quantization of the N H motion enables the discussion of the differences in the IR spectra between the two forms.     

The influence of charges and hydrogen bond on the conformation of zwitterionic 3-(2-hydroxyalkyl-pyridinium)-propionates and their hydrobromides

The effects of intra- and intermolecular electrostatic interactions and hydrogen bonding on the conformation of 3-(2-hydroxymethyl-pyridinium)-propionic acid bromide (1) and 3-(2-hydroxyethyl-pyridinium)-propionic acid bromide (2) have been studied. In 1, the molecules are linked by Br⁻ ion to form two intermolecular hydrogen bonds COOHBrHOCH₂ (O(1)Br=3.175(3) and O(3)Br=3.305(3) Å) yielding chains. The molecules of 2 form centrosymmetric dimers connected by a pair of H-bonds between COOH and CH₂OH groups (O(1)O(3)=2.674(3) Å), and the H-bonded CH₂OH group further interacts with the Br⁻ ion (O(3)Br=3.166(5) Å). In both the compounds, the Br⁻ ion additionally interacts electrostatically with the positively charged nitrogen atom. To analyse these interactions theoretically, the structures of 3-(2-hydroxy-alkyl)pyridinium propionates (betaines) and their hydrogen bromides as monomers and dimers in various configurations are analysed by PM3 and B3LYP/6-31G(d,p) calculations. Although both electrostatic interactions and H-bonds strongly affect the conformation of the investigated compounds, the former effect seems to be dominant. FTIR spectra of 1 and 2 in the solid state are analysed.     

Studies on the phase properties of lyotropic liquid crystals of Brij35/sodium oleate/oleic acid/water system: By means of polarizing microscope, SAXS, 2H-NMR and rheological methods

The pseudo-quaternary phase diagram of Brij35/sodium oleate/oleic acid/water systems has been investigated, and the liquid crystal area has been identified, which covers about two thirds of the whole phase diagram. The liquid crystal structure and behavior have been also studied by using polarizing texture, small angle X-ray scattering, ²H-NMR and rheometer etc. The result shows that when the composition of the system changes along the line of AA’ in this large liquid crystal region, the structural change is cubic→cubic/lamellar→lamellar→lamellar/hexagonal→hexagonal. Meanwhile, we made the first attempt of systematic study of the rheological properties of the above system. The lattice constants of cubic and hexagonal liquid crystals are 10.53 and 5.68 nm, respectively.     

Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.