Imidazole Crystal Research Articles

Deep insight into reasons for the mechanoluminescence phenomenon of triphenylamine-substituted imidazoles and their distinct mechano-fluorochromic behaviours.

Three imidazoles with different numbers of fused aromatic rings have been prepared by the respective introduction of triphenylamine and 4-cyanophenyl at the N1 and C2 positions in the imidazole ring. Each imidazole effectively exhibits positive solvatochromism, and that of benzo[d]imidazole is the most significant. Although these imidazole crystals have centrosymmetric space groups, they are all ML-active. It was verified by DFT calculations based on X-ray crystallography that some molecular couples with strong intermolecular interactions possess large net dipole moments that should be dominantly responsible for the ML behaviours of these crystals. Moreover, the considerably high molecular dipole moments of the three imidazoles also make a great contribution to good ML effects. Based on this triphenylamine-substituted imidazole system, the relationships among space groups, molecular dipole moments, polar molecular couples and the ML phenomenon are made clear for the first time. Unlike the remarkable MFC activities on imidazole and benzo[d]midazole crystals, phenanthro[9,10-d]imidazole is MFC-inert, and this may well be attributed to strong intramolecular C–H⋯π interactions, which make the rotation of triphenylamine nearly impossible under force stimuli.

Intermolecular Interactions in Bromo-, Methyl-, and Cyanoimidazole Derivatives

Materials containing bistable N–H···N hydrogen bonds, such as imidazole crystals, show promise for applications in electronics. Herein, we examine the effect of imidazole functionalization upon structural parameters relating to proton transfer, molecular rotation, and order–disorder transitions. Three different substituents are studied: methyl-, bromo-, and cyano-, resulting in steric, electronic, and supramolecular modification of the imidazole core.

¹H-MAS-NMR chemical shifts in hydrogen-bonded complexes of chlorophenols (pentachlorophenol, 2,4,6-trichlorophenol, 2,6-dichlorophenol, 3,5-dichlorophenol, and p-chlorophenol) and amine, and H/D isotope effects on ¹H-MAS-NMR spectra.

Chemical shifts (CS) of the 1H nucleus in N···H···O type hydrogen bonds (H-bond) were observed in some complexes between chlorophenols [pentachlorophenol (PCP), 2,4,6-tricholorophenol (TCP), 2,6-dichlorophenol (26DCP), 3,5-dichlorophenol (35DCP), and p-chlorophenol (pCP)] and nitrogen-base (N-Base) by solid-state high-resolution 1H-NMR with the magic-angle-spinning (MAS) method. Employing N-Bases with a wide range of pKa values (0.65–10.75), 1H-MAS-NMR CS values of bridging H atoms in H-bonds were obtained as a function of the N-Base’s pKa. The result showed that the CS values were increased with increasing pKa values in a range of ΔpKa < 0 [ΔpKa = pKa(N-Base) - pKa(chlorophenols)] and decreased when ΔpKa > 2: The maximum CS values was recorded in the PCP (pKa = 5.26)–4-methylpyridine (6.03), TCP (6.59)–imidazole (6.99), 26DCP (7.02)–2-amino-4-methylpyridine (7.38), 35DCP (8.04)–4-dimethylaminopyridine (9.61), and pCP (9.47)–4-dimethylaminopyridine (9.61) complexes. The largest CS value of 18.6 ppm was recorded in TCP–imidazole crystals. In addition, H/D isotope effects on 1H-MAS-NMR spectra were observed in PCP–2-amino-3-methylpyridine. Based on the results of CS simulation using a B3LYP/6-311+G** function, it can be explained that a little changes of the N–H length in H-bond contribute to the H/D isotope shift of the 1H-MAS-NMR peaks.

Density functional molecular dynamics simulations investigation of proton transfer and inter-molecular reorientation under external electrostatic field perturbation: Case studies for water and imidazole systems

Proton transfer is a governing factor in the proton exchange efficiency in membrane fuel cells (PEMFCs), which are an alternative environmentally friendly resource. To develop the capacity of the PEMFC system, anhydrous membranes containing imidazole groups have garnered much interest. In this research, the relationship between the hydrogen bond networks, including the consequent packing structure, and the proton conductivity of water and imidazole (Im) systems have been systematically studied. The effect of external electrostatic perturbation was investigated in (H2O)H+⋯H2O, (Im)H+⋯Im, bulk water, and imidazole superlattice systems. In all of these cases, the application of an electric field in a direction opposite to that of the overall system dipole significantly reduces the activation barrier for proton transport. In isolated systems, (H2O)H+⋯H2O and (Im)H+⋯Im, the preferred orientation angle between the neighbouring molecules was 90°. From density functional molecular dynamics simulations of the bulk system, the proton diffusion coefficient was found to increase under the perturbation by the applied electric fields in range of 1.29 × 107 to 3.86 × 107 V cm−1 (0.0025–0.0075 a.u.) for both water and imidazole. To trace the efficient proton transfer, the proton movement trajectory was explicitly analysed in detail. Interestingly, a tilted proton hopping direction was found for imidazole crystal.

A first‐principles investigation of the hydrogen bond interaction and the sensitive characters in cis‐1,3,4,6‐tetranitrooctahydroimidazo‐[4,5‐d]imidazole

AbstractA theoretical study of structural and electronic properties of cis‐1,3,4,6‐tetranitrooctahydroimidazo‐[4,5‐d]imidazole (BCHMX) crystal is performed using density functional theory. The band structure, the total density of states, the atomic orbit projected density of states (PDOS) of C, N, O, and H, and Mulliken population analysis are discussed. The study by analyzing the PDOS shows that the structure of BCHMX crystal possesses CH···O intra‐ and intermolecular hydrogen bonding. There are hydrogen bonds between H3‐1s and O5‐2p orbits, H2‐1s and O6‐2p orbits of intramolecules and between H2‐1s and O1‐2p orbits of intermolecules. The reasons for the smaller impact sensitivity compared with β‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane and 1,3,5‐trinitro‐1,3,5‐triazinane are also explored from the band gap in the crystal and the weakest bond dissociation energy in single molecule. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Experimental charge-density studies, electrostatic and topological analysis of 1-(2′-aminophenyl)-2-methyl-4-nitro-1H-imidazole crystals

Experimental charge-density studies, electrostatic and topological analysis of 1-(2′-aminophenyl)-2-methyl-4-nitro-1<i>H</i>-imidazole crystals

Experimental charge-density studies, electrostatic and topological analysis of 1-(2′-aminophenyl)-2-methyl-4-nitro-1H-imidazole crystals

Experimental charge-density studies, electrostatic and topological analysis of 1-(2′-aminophenyl)-2-methyl-4-nitro-1<i>H</i>-imidazole crystals

Strong coupling effects in the polarized IR spectra of the chain hydrogen bond systems in imidazole crystals: H/D isotopic ‘self-organization’ effects in the IR spectra of isotopically diluted imidazole single crystals

This paper presents the investigation results of the polarized IR spectra of H1245 imidazole crystals and of D1H245, D1245 and H1D245 imidazole deuterium derivative crystals. The spectra were measured using polarized light at the room temperature and at 77 K by a transmission method, for two different crystalline faces. Theoretical analysis of the results concerned linear dichroic effects, H/D isotopic and temperature effects, observed in the spectra of the hydrogen and of the deuterium bonds in imidazole crystals, at the frequency ranges of ν N–H and ν N–D bands. The basic crystal spectral properties can be satisfactorily interpreted in a quantitative way for a hydrogen bond linear dimer model. Such a model explains not only a two-branch structure of the ν N–H and ν N–D bands in crystalline spectra, but also some essential linear dichroic effects in the band frequency ranges, for isotopically diluted crystals. Model calculations, performed within the limits of the strong-coupling model, allowed for quantitative interpretation and for understanding of the basic properties of the hydrogen bond IR spectra of imidazole crystals, H/D isotopic, temperature and dichroic effects included. The results allowed verification of theoretical models proposed recently for the imidazole crystal spectra generation mechanisms. In the scope of our studies, the mechanism of H/D isotopic self-organization processes, taking place in the crystal hydrogen bond lattices, was also recognized. It was proved that for isotopically diluted crystalline samples of imidazole, a non-random distribution of protons and deuterons exclusively occurs in some restricted fragments (domains) of open chains of the hydrogen-bonded molecules. Nevertheless, these co-operative interactions between the hydrogen bonds do not concern adjacent fragments of neighboring hydrogen bond chains in the lattice. Analysis of the isotopic self-organization effects in the spectra of imidazole crystals delivered crucial arguments for understanding of the nature of the hydrogen bond spectra generation mechanisms.

Proton Transfer in Heterocycle Crystals

We study the proton diffusion process in imidazole-based molecular crystals, which are new candidate materials for fuel cell membranes. These materials are characterized by hydrogen bonded networks of molecules, which provide viable routes for the long-range diffusion of protons. By the application of a recently developed, powerful technique to determine reaction pathways in complex systems, we are able to reproduce the diffusion process in the imidazole crystal and in the more complicated and rigid structure of imidazole 2-ethyleneoxide. Our results cast new light on the atomistic details of the molecular rearrangements sustaining the ionic diffusion.

One- and Two-Dimensional 15N Exchange CP/MAS NMR Studies of the Structure and Electronic Properties of the Intermolecular N—H⋯N Hydrogen Bond in Imidazole Crystal

The hydrogen bond of the type N—H⋯N in imidazole crystal has been studied by one- and two-dimensional 15N exchange CP/MAS NMR measurements as well as the powder NMR spectrum. The chemical shift anisotropies for —N= and —N< were determined from the powder 1D spectrum. In 2D exchange CP/MAS NMR spectrum, the cross peaks between the 15N main resonance peaks for —N= and —N< were observed, implying that magnetization exchange between —N= and —N< takes place. The 1D exchange CP/MAS NMR measurements determined the exchange rate of magnetization at 289 K to be 1.3 and 1.5 s−1 for —N= and —N<, respectively. The proton-driven spin-diffusion model interprets the experimental values, and the exchange rate depends strongly on the RF power of the proton decoupling field, suggesting that the magnetization transfer between —N= and —N< takes place by the 1H-driven spin-diffusion mechanism.

A resonance model for the [formula omitted] and vX-H vibrations in the bent H-bonds, for interpretation of the [formula omitted] vibration first overtone band shapes in the IR: The imidazole crystal

In this paper we attempt to explain spectral effects measured in the IR spectra of a number of the H-bonded crystals, which appear in the frequency range corresponding to the overtone bands of the γ X− H + … Y (“bending-out-of-plane”) vibrations and are connected with considerable intensities of the overtone bands. We also attempt to explain the observed fine structure of these bands and a strong temperature effect. We consider a simple model of coupling between the two proton vibrations in the H-bonds of the crystalline lattices of imidazole and adipic acid, formally similar to the Fermi resonance model. However, we rather exclude anharmonicity of the protonic vibrations in the H-bonds as a source of the spectral effects analyzed, ascribing spectral phenomena to the effective geometry change (i.e. bending) of the H-bonds in the crystals. Such an approach allows us to explain temperature effects in the crystalline spectra, i.e. to predict the decrease of the coupling energy values with growing temperatures. Model calculations demonstrate that the appearance of the overtone band fine structure is related to the v X-H band fine structure and the γ X− H + … Y band shape depends on the intensity in each individual v X-H band. The analyzed mechanism is a kind of transfer of the “strong-coupling” mechanism onto the proton bending vibrations in the H-bonds, which—due to their highly harmonic nature— do not participate in this sort of interaction.

Strong-coupling mechanism for interpretation of the IR spectra of the hydrogen bonded imidazole crystal

In this work we have attempted to provide a new interpretation of some complex spectral effects, recently observed in the high frequency region of the IR spectra of hydrogen bonded imidazole crystals. The subjects of our interest were effects corresponding to the intensity distribution, the linear dichroism, the influence of temperature and the isotopic substitution of deuterium in imidazole molecules, measured in the v NH and the v ND band ranges in the crystalline spectra. Based on model calculations it was shown that the “strong-coupling” model was able to quantitatively reproduce the v NH and v ND band shapes in the spectra of the imidazole crystal. This fact can be considered as a basis for an explanation of the isotopic, polarization and temperature effects in the spectra. The Fermi resonance effects have been found to be of a minor importance. The key property of the crystal responsible for the abnormal spectral properties of its H-bonds seems to be the statistical disorder in the crystalline lattice, due to bending of the H-bonds. This structural effect, along with the very specific selection rules in the IR for the centrosymmetric H-bonded dimers and the correlation field interactions in the crystal, were considered to be the main source of the spectral effects analyzed.

Strong-coupling mechanism for interpretation of the IR spectra of the hydrogen bonded imidazole crystal

In this work we have attempted to provide a new interpretation of some complex spectral effects, recently observed in the high frequency region of the IR spectra of hydrogen bonded imidazole crystals. The subjects of our interest were effects corresponding to the intensity distribution, the linear dichroism, the influence of temperature and the isotopic substitution of deuterium in imidazole molecules, measured in the νN H and the ν N D band ranges in the crystalline spectra. Based on model calculations it was shown that the “strong-coupling” model was able to quantitative reproduce the ν N H and ν N D band shapes in the spectra of the imidazole crystal. This fact can be considered as a basis for an explanation of the isotopic, polarization and temperature effects in the spectra. The Fermi resonance effects have been found to be of a minor importance. The key property of the crystal responsible for the abnormal spectral properties of its H-bonds seems to be the statistical disorder in the crystalline lattice, due to bending of the H-bonds. This structural effect, along with the very specific selection rules in the IR for the centrosymmetric H-bonded dimers and the correlation field interactions in the crystals, were considered to be the main source of the spectral effects analyzed.

H-bonds of imidazole crystals. I. Measurements of polarized light IR spectra

This article is the first of a series on the v s bands of imidazole crystals. It deals with experimental results on fully protonated and N—D deuterated species. We first describe the experimental conditions which enable us to obtain polarized spectra of monocrystals of imidazole which are sufficiently thin (≈1 μm) to give non-saturated v s bands, so that we can measure with good precision the first moments of the v s bands of these two species at various temperatures ranging from 10 to 300 K.

H-bonds of imidazole crystals. II. Determination of the magnitudes of the various anharmonic couplings of vs modes

In this article results given in a previous paper (part I), concerning the spectra of NH and ND species recorded with a polarization parallel to the c axis are analyzed, the necessary corrections on the raw data performed, v s bands and their first moments are then compared with corresponding quantities predicted from a simple theory which describes quantitatively the anharmonic interactions of a single H-bond with a low frequency vibration of the same H-bond and with binary combinations of modes (Fermi resonances). This allows us to determine the magnitudes of the various anharmonic interactions involved. It appears that the low frequency vibration which modulates v s is a bending mode of the H-bond (NH ↑ … N), a finding somewhat unexpected, as this low frequency vibration is usually thought to be the stretching vibration v σ of the H-bond ▪

Dynamics of organic molecular crystals

Specific aspects of organic molecular crystal dynamics are emphasized. Details of the spectra of acenaphthene, phenanthrene and imidazole crystals are discussed.

Lattice Vibrations of Imidazole Crystals

Abstract Polarized low-frequency Raman spectra of imidazole single crystals were measured with a He-Ne laser source. A new band at 172 cm−1 (Bg) was observed. An assignment for the lattice vibrations of imidazole crystals is proposed on the bases of this Raman data and far-infrared spectral data of Perchard and Novak, as well as the preliminary results calculated from Harada's and Williams' potentials.

ChemInform Abstract: ESR AND ENDOR STUDIES OF THE MAIN RADICAL CREATED BY GAMMA IRRADIATION AT 300 K IN THE IMIDAZOLE CRYSTAL

Chemischer InformationsdienstVolume 5, Issue 3 Physical Organic Chemistry ChemInform Abstract: ESR AND ENDOR STUDIES OF THE MAIN RADICAL CREATED BY GAMMA IRRADIATION AT 300 K IN THE IMIDAZOLE CRYSTAL B. LAMOTTE, B. LAMOTTESearch for more papers by this authorP. GLOUX, P. GLOUXSearch for more papers by this author B. LAMOTTE, B. LAMOTTESearch for more papers by this authorP. GLOUX, P. GLOUXSearch for more papers by this author First published: January 22, 1974 https://doi.org/10.1002/chin.197403064AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume5, Issue3January 22, 1974 RelatedInformation

ESR and ENDOR studies of the main radical created by gamma irradiation at 300 °K in the imidazole crystal

ESR studies of room-temperature gamma irradiated single crystals of imidazole and of its derivatives deuterated in several different positions have permitted us to identify the main radical produced by such irradiation. It is a π radical formed by the addition of one hydrogen atom on a carbon of the ring. Moreover, we show that the hydrogen atom which is added to form the radical comes from hydrogens involved in the hydrogen bond chains. The subsequent ENDOR study enables us to deduce the spin density distribution in the radical from the determination of all the proton hyperfine tensors.

Hydrogen-bond vibrations in the external Raman spectrum of imidazole single crystals

Librational and translational modes of crystalline imidazole are active in the low-frequency Raman spectrum of this crystal. Librational modes have been assigned by the oriented gas model, which is particularly suitable for calculating the intensity matrices. Translational modes contain intermolecular N H⋯ N hydrogen-bond vibrations. The assignment of translational modes has been made assuming two types of motion: intrachain and interchain. This separation of translation modes makes it possible to assign intermolecular hydrogen-bond vibrations in the imidazole crystal.