Irena Majerz

First O−H−N Hydrogen Bond with a Centered Proton Obtained by Thermally Induced Proton Migration

Within a range of 0.1 Å, the H atom in the O-H-N hydrogen bond of the adduct 4-methylpyridine⋅pentachlorophenol could be shifted by a simple adjustment of temperature. At approximately 90 K the H atom is exactly centered between the O and the N atoms, as could be shown by stepwise monitoring by using variable-temperature single-crystal neutron diffraction.

Structure and spectroscopic properties of the 1:1 complex of 4-methylpyridine with pentachlorophenol

Abstract The structure of the complex of 4-methylpyridine with pentachlorophenol (MPPCP) has been determined by X-ray diffraction methods. The crystals are triclinic, space group P 1 , with a = 7.408(6), b = 8.934(7), c = 13.653(9) A, α = 100.15(6), β = 118.50(6), γ = 103.67(6)° and Z = 2. The structure solved by the direct methods has been refined to R = 0.026 for 1466 independent reflections. The CO bond length of 1.314(4) a, which is an average literature value for phenol and phenolate bond distances and the O⋯H⋯N hydrogen bond distance of 2.552(4) A, together with IR and UV spectroscopic data, seem to show that the proton in the hydrogen bridge of MPPCP is described by an unsymmetrical double minimum potential energy curve with the vibrational ground level penetrating the top of the barrier.

Flexible ferroelectric organic crystals.

Flexible organic materials possessing useful electrical properties, such as ferroelectricity, are of crucial importance in the engineering of electronic devices. Up until now, however, only ferroelectric polymers have intrinsically met this flexibility requirement, leaving small-molecule organic ferroelectrics with room for improvement. Since both flexibility and ferroelectricity are rare properties on their own, combining them in one crystalline organic material is challenging. Herein, we report that trisubstituted haloimidazoles not only display ferroelectricity and piezoelectricity—the properties that originate from their non-centrosymmetric crystal lattice—but also lend their crystalline mechanical properties to fine-tuning in a controllable manner by disrupting the weak halogen bonds between the molecules. This element of control makes it possible to deliver another unique and highly desirable property, namely crystal flexibility. Moreover, the electrical properties are maintained in the flexible crystals.

Structural manifestations of proton transfer in complexes of 2,6-dichlorophenols with pyridines

DFT B3LYP/6-31G(d,p) calculations were performed to describe the proton transfer reaction pathway in the 2,6-dichlorophenolate of pyridine. The aim of these calculations was to establish the character of the dependence of the structure parameters on the proton transfer and comparing the results with known structures, e.g. the 2,6-dichloro-4-nitro- and pentachlorophenolates of pyridines. To make this comparison more reliable, the calculations were repeated with the use of a reaction-field correction with the Onsager radius and electric permittivity taken from the solid-state measurements. The calculations show that the second approach gives a better description of the structural modifications during the proton transfer.

The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

Abstract The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MPPCP) and its deuterated analogue (MPPCP-d) were determined at 80 K by X-ray diffraction. The MPPCP complex crystallizes in the space group P 1 with a = 7.267(7), b = 8.966(9), c = 13.110(14) A , α = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MPPCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12) A , β = 101.38(9)° and Z = 4. The O…H…N bridge bond distance of 2.515(4) A is significantly shorter than that determined at room temperature (2.552(4) A) and the OD…N bond length of 2.628(6) A is only slightly shorter than at room temperature (2.638(3) A). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.

An unusual geometrical and spectroscopic isotopic effect in the solid complex of 4-methylpyridine with pentachlorophenol

Abstract The structure of the complex of 4-methylpyridine with deuterated pentachlorophenol (MP PCP-d) has been determined by X-ray diffraction. The crystals are monoclinic, space group Cc, with a=3.942(3), b=27.73(3), c=13.297(9) A,β=101.81(6)° and Z=4. The structure, solved by direct methods, has been refined to R=0.036 for 3600 non-zero (hkl) ( h k l ) reflections. The crystals of MP PCP-d are non-isomorphous with the complex MP PCP. The OD group is engaged in a bifurcated interaction to give OD⋯N and OD⋯Cl(6) hydrogen bonds with lengths 2.638(3) and 3.002(3) A and angles 141(4) and 115(4)°, respectively. The anomalous spectroscopic isotopic ratio ν )OHN)/ν(ODN) is lower than 1 and has been explained by drastic changes in the hydrogen bridge geometry.

On a hard/soft hydrogen bond interaction

Abstract Various physical properties of AH⋯B hydrogen bonded complexes are analyzed from the point of view of possible proton transfer processes. As a general parameter of the proton-donor–acceptor ability of interacting components the normalized ΔpKN=ΔpKa−ΔpKa(crit) parameter was assumed, where ΔpKa=pKa(B+H)−pKa(AH). ΔpKa(crit) refers to the range where the proton transfer degree reaches 50%. Two kinds of correlations between the given physical property and ΔpKN can be distinguished: of sigma and delta type. To the first one belong dipole moments, 15N NMR chemical shifts, NQR frequencies and the bond lengths in the solid state, while to the second one infra-red protonic band positions, their intensities and 1H NMR chemical shift. A general equation expressing the relationship between any physical property and ΔpKN was derived in which the central factor exp(2.303ξΔpKN) describes the behavior in the critical region. It has been shown that the ξ parameter can be used for the expression of the hardness. The value of this parameter is the higher the harder is interaction its maximum being equal 1. This measure very well correlates with the polarizability in transition state of hydrogen bonds. The detailed analysis of data in literature collected so far shows a good agreement of estimated ξ values by using different physical properties. The influence of various factors on the ξ value is discussed. Most important are chemical properties of interacting components but it was clearly shown the importance of the environment. With increasing permittivity a marked augmentation of the ξ parameter is generally observed.

Isotopic effect on 35Cl NQR spectra of pentachlorophenol-amine hydrogen-bonded complexes

Abstract The 35 Cl NQR frequencies for a number of deuterated and non-deuterated pentachlorophenol-amine complexes were studied over a broad Δp K a range covering both non-proton-transfer (HB) and proton-transfer (PT) states. The HB complexes show a positive and PT a negative deuteration effect upon ν NQR frequencies. The observed effect corresponds with the change of the hydrogen bond polarity of the order of 0.3 D. For the 4-methylpyridine complex which is located within the inversion (critical) range, the anomalous effect related to the change of the lattice symmetry was found.

Structure and spectroscopic behaviour of the solid adduct of 3-methylpyridine with 2,6-dichloro-4-nitrophenol

Abstract The structure of the adduct of 3-methylpyridine with 2,6-dichloro-4-nitrophenol has been determined by X-ray diffraction. The crystals are monoclinic, space group P 2 1 / c with a = 7.935(2), b = 23.789(7), c = 7.521(2)A, β = 112.44(2)° and Z = 4. The structure solved by direct methods was refined to R = 0.040 for 1564 non-zero independent reflections. The complex is characterized by one of the shortest NH⋯O hydrogen bridges with the N⋯O distance equal to 2.544(4)A. Both the estimated localization of the proton and the CO bond length (1.285(4)A) indicate that the proton is transferred from oxygen to nitrogen. In contrast, the UV and IR spectra imply a double minimum potential for the proton motion.

Directionality of Inter- and Intramolecular OHO Hydrogen Bonds: DFT Study Followed by AIM and NBO Analysis

The directionality of inter- and intramolecular OHO hydrogen bonds has been compared. For intramolecular bridges it is determined by an orbital formed in the proton transfer process. For intermolecular bonds, the hydrogen-bonded proton is attached to two lone pairs of the acceptor and the OHO angle is not fixed but can change in a broad range. Depending on the OHO angle, the interaction changes continuously from electrostatic interaction to strong OHO hydrogen bond.