A unified quantum model susceptible to elucidate the dissimilarity of IR spectral density of dicarboxylic acid crystals: Phthalic and terephthalic acid crystals cases.

Over the last decades, several approaches have been developed for elucidating the infrared spectral density of dicarboxylic acid crystals, which has been served as prototype for determining hydrogen bonds dynamics. These approaches differ in how accurately the simulated spectra can superimpose the experimental ones. In this study, we present a superdimer quantum approach susceptible to elucidate the infrared spectral properties of some particular dicarboxylic acid crystals using a newly proposed algorithm, which favors the rule of Davydov coupling in the generation of the spectra.

Molecular docking studies, structural and spectroscopic properties of monomeric and dimeric species of benzofuran-carboxylic acids derivatives: DFT calculations and biological activities.

Structural optimization, molecular docking analysis, electronic and vibrational properties have been investigated for the 1-benzofuran-2-carboxylic acid (2BF) and 1-benzofuran-3-carboxylic acid (3BF) using DFT/B3LYP/6-311++G(d,p) level of theory. The theoretical parameters have a very good consistency with the experimental ones. The weak intermolecular interactions were analyzed by different tool such as: Hirshfeld surfaces, topological analysis and natural bond orbital studies.

How far the vibrational exciton interactions are responsible for the generation of the infrared spectra of oxindole crystals?

Oxindole (indolin-2-one, Ox) is a unique and a crucial molecular system in spectroscopic studies. Indole is the core structure of many substances found in the human body (tryptophan, serotonin) and the indole alkaloids have highly differentiated pharmacological properties such as analgesic, anti-fever and anti-inflammatory. The Ox's structural results given in the Cambridge Structural Database revealed the existence of only one crystalline form of Ox, referred to the α-form.

Electrical anharmonicity in hydrogen bonded systems: complete interpretation of the IR spectra of the Cl-H[combining right harpoon above] stretching band in the gaseous (CH)OHCl complex.

Following the previous developments to simulate the fully infrared spectra of weak hydrogen bond systems within the linear response theory, an extension of the adiabatic model is presented here. A general formulation including the electrical anharmonicities in the calculation of the damped autocorrelation function of weak H-bonds is adopted to facilitate the support of the additional properties, and thus the IR spectra of the Cl-H[combining right harpoon above] stretching band in the gaseous (CH)OHCl complex. We have explored the origins of the broadening of the Cl-H[combining right harpoon above] stretching band.

"Long-distance" H/D isotopic self-organization phenomena in scope of the infrared spectra of hydrogen-bonded terephthalic and phthalic acid crystals.

This paper deals with the experimental and theoretical studies of abnormal properties of terephthalic acid (TAC) and phthalic acid (PAC) crystals manifested in the H/D isotopic exchange. The widely utilized deuteration routine appeared to be insufficiently effective in the case of the h-TAC isotopomer. In the case of the d-TAC derivative the isotopic exchange process occurred noticeably more effectively.

Long-distance inter-hydrogen bond coupling effects in the polarized IR spectra of succinic acid crystals.

The spectral properties of four different crystalline succinic acid (HOOC-(CH2)2-COOH) (SAC) isotopomer systems, h6, d2, d4 and d6, were examined by means of the IR spectroscopy in polarized light aided by numerical simulations of the νO-H and νO-D band contour shapes on utilizing the "strong-coupling" model. The abnormal IR spectral properties of SAC crystals in relation to the corresponding properties of glutaric, pimelic and adipic acid crystals were ascribed to the hyperconjugation electronic effects in the acid associated molecules. A vibronic coupling mechanism involving the proton stretching vibrations in the (COOH)2 cycles and the electronic motions in the molecular skeletons, the isotopic "H/D self-organization" mechanisms and a long-distance vibrational exciton coupling between the adjacent (COOH)2 cycles in the molecular chains are mainly responsible for the generation of the temperature effects in the crystalline IR spectra.

H/D isotopic recognition and temperature effects in IR spectra of hydrogen-bonded cyclic dimers in crystals: 3-methylcinnamic acid and 4-phenylbutyric acid.

In the present work, the experimental and theoretical study of the nature of the inter-hydrogen bond interactions in two different carboxylic acids, 3-methylcinnamic acid (3MCA) and 4-phenylbutyric acid (4PBA), were reported. The polarized IR spectra of 3MCA and 4PBA crystals were recorded at the frequency ranges of the νO-H and νO-D bands. The spectral properties of 3MCA and 4PBA interpreted with the aid of the calculations based on the "strong-coupling" model.

Inter-hydrogen bond coupling in crystals with molecular chains in their lattices investigated by polarized IR spectroscopy: 4-Bromo-3,5-dimethylpyrazole and 3,4-dimethoxyphenylacetic acid.

We report the results of the experimental and theoretical studies of the polarized IR crystalline spectra of 4-bromo-3,5-dimethylpyrazole (4Br35DMPz) and 3,4-dimethoxyphenylacetic acid (34DMPAA) as well as the spectra of their deuterium-bonded analogues. The results of model calculations of the temperature impact exerted on to the band shapes measured in the X-H- and X-D bond stretching vibration regions, performed on the basis of the "strong-coupling" model, are also shown. These studies confirm a direct relationship between the spectral properties in IR and the electronic structure of the associating molecules in the crystals.

Inter-hydrogen bond coupling in crystals of 3-phenylpyrazole polymorphs investigated by polarized IR spectroscopy.

The remarkably strong differences in the fine structure patterns of the νN-H and νN-D bands, temperature and H/D isotopic effects in crystals of two 3-phenylpyrazole (3PhPz) polymorphs, with tetrameric and hexameric hydrogen bond aggregates, were examined by polarized IR spectroscopy, aided by the calculations utilizing the "strong-coupling" model. Experimental and theoretical approaches have suggested that the anti-co-operativity of hydrogen bonds is the main factor responsible for the differences in the spectral properties of both polymorphs. This interaction affects hydrogen-bond geometry of the associates constituting the lattices and in consequence decides about the relative contribution of two different exciton coupling mechanism, "through-space" (SS) and "tail-to-head" (TH), in the spectra generation.

A complete assignment of the vibrational spectra of 2-furoic acid based on the structures of the more stable monomer and dimer.

The structural and vibrational properties of cyclic dimer of 2-furoic acid (2FA) were predicted by combining the available experimental infrared and Raman spectra in the solid phase and ab initio calculations based on density functional theory (DFT) with Pople's basis sets. The calculations show that there are two cyclic dimers for the title molecule that have been theoretically determined in the gas phase, and that only one of them, cis conformer, is present in the solid phase. The complete assignment of the 66 normal vibrational modes for the cis cyclic dimer was performed using the Pulay's Scaled Quantum Mechanics Force Field (SQMFF) methodology.

Temperature, H/D isotopic and Davydov-splitting effects in the polarized IR spectra of hydrogen bond chain systems: 1,2,4-Triazole and 3-methyl-2-oxindole crystals.

The spectral properties of two different hydrogen-bonded crystalline systems, 1,2,4-triazole and 3-methyl-2-oxindole, containing molecular chains in their lattices, were examined by polarized IR spectroscopy, aided by the calculations utilizing the "strong-coupling" model. The experimental and theoretical approaches have shown that the individual crystal spectral properties in IR remain in a close relation with the electronic structure of the individual molecular systems. A vibronic coupling mechanism involving the hydrogen bond protons and the electrons occupying the π-electronic orbitals in the molecules determines the way in which the vibrational exciton coupling between the hydrogen bonds in the crystals occurs.

H/D isotopic and temperature effects in the polarized IR spectra of hydrogen-bond cyclic trimers in the crystal lattices of acetone oxime and 3,5-dimethylpyrazole.

Polarized IR spectra of hydrogen-bonded acetone oxime and 3,5-dimethylpyrazole crystals were measured at 293 and 77 K in the ν(X-H) and ν(X-D) band frequency ranges. These crystals contain molecular trimers in their lattices. The individual crystal spectral properties remain in a close relation with the electronic structure of the two different molecular systems.

Temperature and H/D isotopic "self-organization" effects in the IR spectra of the hydrogen bond tetramer systems in 3,5-diphenylpyrazole and 4-methyl-1,2,4-triazolethione crystals.

Polarized IR spectra of hydrogen-bonded 3,5-diphenylpyrazole and of 4-methyl-1,2,4-triazolethione crystals were measured at 293 and 77 K in the νN-H and νN-D band frequency ranges. These crystals contain molecular tetramers in their lattices. The individual crystal spectral properties remain in close relation with the electronic structure of the two different molecular systems.

H/D isotopic recognition mechanism in hydrogen-bonded crystals of 3-methylacetanilide and 4-methylacetanilide.

Polarized IR spectra of 3- and 4-methylacetanilide as well as their deuterium derivative crystals were measured at 293K and at 77K by a transmission method. The obtained results were interpreted within the limits of the "strong-coupling" theory. This approach facilitated the understanding of the H/D isotopic, temperature and dichroic effects observed in the hydrogen bond IR spectra.

Polarized IR spectra of the hydrogen bond in 2-thiopheneacetic acid and 2-thiopheneacrylic acid crystals: H/D isotopic and temperature effects.

Polarized IR spectra of 2-thiopheneacetic acid and of 2-thiopheneacrylic acid crystals were measured at 293 and 77 K in the υ(O-H) and υ(O-D) band frequency ranges. The corresponding spectra of the two individual systems strongly differ, one from the other, by the corresponding band shapes as well as by the temperature effect characterizing the bands. The crystal spectral properties remain in close relation with the electronic structure of the two different molecular systems.

H/D isotopic recognition in hydrogen bonded systems: H/D isotopic self-organization effects in the IR spectra of the hydrogen bond in 2-methylimidazole crystals.

Polarized IR spectra of H12(3)45 2-methylimidazole and of its H1D2(3)45, D1H2(3)45 and D12(3)45 deuterium derivative crystals are reported and interpreted within the limits of the "strong-coupling" theory. The spectra interpretation facilitated the recognition of the H/D isotopic "self-organization" phenomenon, which depends on a non-random distribution of protons and deuterons in the lattices of isotopically diluted crystal samples. The H/D isotopic "self-organization" mechanism engaged all four hydrogen bonds from each unit cell.

Polarized IR spectra of the hydrogen bond in two different oxindole polymorphs with cyclic dimers in their lattices.

This article focuses on the problem of remarkably strong changes in the fine structure patterns of the ν(N-H) and ν(N-D) bands attributed to the hydrogen and deuterium bonds accompanying the phase transition, which occurs between two polymorphic forms of oxindole. The lattices of these two different crystals contain hydrogen-bonded cyclic dimers differ in their geometry parameters. The source of these differences in the polymorph spectral properties results from the geometry relations concerning the dimers constituting the lattice structural units.

Effect of the resonance of the C-H and O-H bond stretching vibrations on the IR spectra of the hydrogen bond in formic and acetic acid.

It is shown that the resonance of the O-H and C-H bond stretching vibrations is responsible for a noticeable intensity redistribution effect in the IR spectra of associated formic acid molecules in the gaseous phase. This effect is manifested by a considerably high growth in intensity of the νC-H band, which overlaps the νO-H band contour in the spectra. A vibronic coupling of the Herzberg-Teller-type expressed by the second order term in the perturbation theory is the most probable source of these spectral effects.

H/D isotopic recognition in hydrogen-bonded systems: strong dynamical coupling effects in the polarized IR spectra of 3-methylthioacetanilide and 4-methylthioacetanilide crystals.

This paper presents the investigation results of the polarized IR spectra of the hydrogen bond in crystals of 3- and 4-methylthioacetanilide. The spectra were measured at 293 and 77 K by a transmission method, with the use of polarized light. The main spectral properties of the crystals can be interpreted satisfactorily in terms of the "strong-coupling" theory, on the basis of the hydrogen bond centrosymmetric dimer model.

Effects of dynamical couplings in IR spectra of the hydrogen bond in N-phenylacrylamide crystals.

This article presents the investigation results of the polarized IR spectra of the hydrogen bond in N-phenylacrylamide crystals measured in the frequency range of the proton and deuteron, ν(N-H) and ν(N-D), stretching vibration bands. The basic spectral properties of the crystals were interpreted quantitatively in terms of the "strong-coupling" theory. The proposed model of the centrosymmetric dimer of hydrogen bonds facilitated the explanation of the well-developed, two-branch structure of the ν(N-H) and ν(N-D) bands as well as the isotopic dilution effects in the spectra.

Electron-induced phase transition in hydrogen-bonded solid-state 2-pyridone.

This paper presents the results of experimental studies of hydrogen-bonded 2-pyridone crystal IR spectra. Spectral studies have demonstrated the existence of two anhydrous solid-state phases of each compound, namely the α and the β phases. Hydrogen bonds in the high-temperature α phase of these crystals have been estimated to be 40% stronger than the hydrogen bonds in the β phase, which are stable at room temperature.

Investigations of interhydrogen bond dynamical coupling effects in the polarized IR spectra of acetanilide crystals.

This Article presents the investigation results of the polarized IR spectra of the hydrogen bond in acetanilide (ACN) crystals measured in the frequency range of the proton and deuteron stretching vibration bands, nu(N-H) and nu(N-D). The basic spectral properties of the crystals were interpreted quantitatively in terms of the "strong-coupling" theory. The model of the centrosymmetric dimer of hydrogen bonds postulated by us facilitated the explanation of the well-developed, two-branch structure of the nu(N-H) and nu(N-D) bands as well as the isotopic dilution effects in the spectra.

Theoretical modeling of infrared spectra of the hydrogen and deuterium bond in aspirin crystal.

An extended quantum theoretical approach of the nu(X-H) IR lineshape of cyclic dimers of weakly H-bonded species is proposed. We have extended a previous approach [M.E.

Polarized infrared spectra of the H(D) bond in 2-thiophenic acid crystals: a spectroscopic and computational study.

Polarized IR spectra of the hydrogen bond in 2-thiophenic acid crystals, isotopically neat and of mixed H/D isotopic content, are measured at 298 and 77 K in the "residual" nuO-H and nuO-D band frequency ranges. This crystalline system provides spectra in these band frequency ranges that differ considerably in intensity distribution from the spectra of other H-bonded centrosymmetric dimeric species. This change in the spectral properties of the crystals is probably due to the influence of the sulfur atoms from the thiophene aromatic rings, which are directly linked to the (COOH)2 or (COOD)2 cycles.

Experimental and theoretical study of the polarized infrared spectra of the hydrogen bond in 3-thiophenic acid crystal.

This article presents the results of experimental and theoretical studies of the v(O-H) and v(O-D) band shapes in the polarized infrared spectra of 3-thiophenic acid crystals measured at room temperature and at 77 K. The line shapes are studied theoretically within the framework of the anharmonic coupling theory, Davydov coupling, Fermi resonance, direct and indirect damping, as well as the selection rule breaking mechanism for forbidden transitions. The adiabatic approximation allowing to separate the high-frequency motion from the slow one of the H-bond bridge is performed for each separate H-bond bridge of the dimer and a strong nonadiabatic correction is introduced via the resonant exchange between the fast-mode excited states of the two moieties.