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Struktura a nieelastyczne rozpraszanie neutronów przez kryształy molekularne z wiązaniami wodorowymi

Rok M., Bator G., Sobczyk L.

Wiadomości Chemiczne

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2017

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[Z] 71, 7-8

533--557

EN

The molecular crystals, which are built of organic or organic-inorganic molecules, are characterized by the weak intermolecular interactions. From the viewpoint of the potential applications in electronics or optoelectronics the electric properties of the crystals are essential. In turn these properties are related to their crystal structure as well as the dynamics of the molecules in the solid state. The existence of the hydrogen bonds in the crystal structures, conventional and unconventional, is crucial from the viewpoint of the electric properties of the crystals. The dynamics of methyl groups present in the structure can be a measure of the molecular interactions in the crystals. In this work the dynamical properties, first of all taking into account the research results concerning the neutron scattering, will be discussed. The neutron technique is very effective as regards the methyl group dynamics investigations. The relationship between a formation of the conventional and unconventional hydrogen bonds and a tunneling of the methyl groups at low temperature will be discussed. The method of the interpretation of the INS spectra will be described taking into account the theoretical model, the parameters of which are fitted to the experimental data. The examples will regard the following molecular crystals: p-N,N’-1,10-tetraacethyldiaminodurene (TADD) (Figs. 2 and 4), 2,3,5,6-tetramethylpyrazine with chloranilic acid (TMP·CLA) (Figs. 5, 6 and 7), 2,3,5,6- tetramethylpyrazine with bromanilic acid (TMP·BRA) (Figs. 5 and 6) and the crystal of 3,4,7,8-tetramethylphenantroline (Me4phen) and its complex with picric acid (Me4phen·PIC) (Figs. 8 and 9). In this paper we have shown that the surrounding of the methyl group and its interactions with the adjacent molecules has a stronger effect than the changes in the electronic charge density in the molecule.

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Silne wiązania wodorowe w kompleksach wybranych kwasów organicznych z tetrametylopirazyną

Bator G., Sobczyk L.

Wiadomości Chemiczne

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2011

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[Z] 65, 9-10

869-885

EN

In the present review our interest is focused on the hydrogen bonded complexes of tetramethylpyrazine (TMP) with strong proton donors, in particular with chloranilic (CLA) or squaric (H2SQ) acid. The x-ray diffraction studies show that, depending on the proton donor, various assemblies with the acid are formed, e.g. the infinite O-H…N hydrogen bonded chains without proton transfer in the case of the complex with CLA. On the other hand with H2SQ the assemblies of [HSQ]2 2–-2TMPźH+ composition are created, in which the ionized HSQ–1 molecules are present in the form of dimers. These dimers are bound with the TMPźH+ cations on its both sides via the +N-H…O– hydrogen bonds. Picric acid forms with TMP the complex of the 2:1 composition with a double protonated TMP molecule. In the case of HI3 acid the interesting units of the (TMPźH+)2źTMP composition are formed, in which two TMPźH+ cations are coordinated with one TMP molecule through the +N-H…N bridges. In the infrared spectra of the TMP complexes, both with CLA and H2SQ, the similar absorption continua are observed. They can be interpreted in terms of an asymmetric potential for the proton motion, with either the double minimum or the single broad minimum potential for the CLA and H2SQ complexes, respectively. An analysis of the neutron scattering spectra concerns the phenomena of the tunneling splitting, quasielastic neutron scattering (QNS) and inelastic (INS) scattering. In the case of tunneling splitting neat TMP does not show any tunneling transitions in the ěeV energy region, because they are overlapped by the elastic scattering band. In the case of the TMPźCLA complex four tunneling transitions are seen corresponding to the four crystallographically nonequivalent CH3 groups in the TMP molecule. In the spectrum of the complex with squaric acid the observed two transitions are ascribed to the two different CH3 groups. The two remaining CH3 group tunneling transitions are overlapped by the elastic scattering. The measurements in various low temperature ranges yield information about the shape of the CH3 group rotational potential. The shape of the potential is also reflected in the spectra of quasielastic scattering. In particular the temperature dependence of the quasielastic band allows us to find the activation energy for the CH3 rotations. Finally the inelastic neutron scattering spectra are analyzed in the energy range of the CH3 torsional modes (below 200 cm–1 = 25 meV). The analysis shows that for the complexes the torsional vibration frequencies are markedly lower than those for neat TMP. In the case of the TMPźCLA complex frequencies found are particularly low. They are close to the frequencies calculated for the TMP+ cation. A general conclusion can be drawn that in the complexes the CH3 groups behave more loosely than in neat TMP.

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Assembly of Protonated Tetramethylpyrazine (TMP) in Triiodide. Vibrational Spectra and DFT Simulations

Sobczyk L., Bator G., Sawka-Dobrowolska W., Nowicka-Scheibe J., Grech E., Pawlukojć A.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 5

957-963

EN

In the complex of tetramethylpyrazine (TMP) with HI3 two protonated molecules of TMP form the assembly of composition (TMP×H+)2TMP(I3 - )2. The X-ray structure, determined at 100 K, shows the +N-H×××N hydrogen bonds markedly shorter than those found previously [13] at room temperature (2.828 ni s. 2.894 A). The DFT calculations for isolated cation yield the value of 3.038 capital A, ring that reflects the soft ness of the hydroen bond potential. The calculations of vibrational frequencies for crystalline state reflect very well the IR spectra. This relates particularly to the ni (NH+) mode. A remark able discrepancy is observed when calculations are performed for isolated assemblies.

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2'-Hydroxybenzylideneanilines and 2-Hydroxyazobenzenes. The Role of Intramolecular O–HźźźN Resonance Assisted Hydrogen Bonds

Majewska P., Rospenk M., Sobczyk L.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 5

709-721

EN

A short review on the effect of the OH groups in the ortho position on the liquid crystalline properties of benzylideneanilines and azobenzenes is presented. Numerous examples show that there are no general rules governing the behaviour of these compounds. How ever one finds most frequently a broadening of the existence range of mesophases both due to a decrease of freez ing temperature and an increase of the isotropisation temperature. In contrast, the presence of strongly polar groups such as –NO2 and –CN leads to a reverse be haviour that can be explained by as suming a strong pi-electron conjugation of these groups with the conjugate-chelatering formed by intramolecular O–HźźźN hydrogen bond. These rings are analyzed by us ing data related to the structure of molecules and infrared spectra in the region of the stretch ing ni(OH) and bend ing delta(OH) and gamma(OH) modes.

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Structure and Vibrational Spectra of the 1:1 Squaric Acid (H2SQ) – Tetramethylpyrazine (TMP) Adduct

Nowicka-Scheibe J., Grech E., Sawka-Dobrowolska W., Bator G., Sobczyk L.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 5-6

643-652

EN

The crystal structure of the title complex was determined at 100 K by X-ray diffraction. It consists of double ionized dimeric (HSQ)2 2 species and protoned TMPH+ cations. Strong charge assisted (OHO)– and (NHO)+ hydrogen bonds are the main factor of crystal packing. A wealth of unconventional C–HO and C–HN relatively short bridges should be emphasized. Particularly important are the latter ones binding two adjacent TMPH+ cations. The structure is well manifested in the IR and Raman spectra, particularly in the region of (OH) and (NH) as well as of (C=O) frequencies. The complexation of TMPleads to a marked change in the low and high frequency vibrations of the methyl groups. An anomaly on the DSC runs has been found at 163/175 K (cooling/ heating) which can be assigned to the freezing of the methyl group rotations. No change of the crystal symmetry is observed at this temperature.

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On a New Unexpected Benzoxazino-Benzoxazine Derivative

Nowicka-Scheibe J., Sośnicki J. G., Grech E., Głowiak T., Sobczyk L.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 11

1419-1426

EN

The reaction between 2-amino-5-nitrophenol and 1,2-cyclohexanedione in ethanol leads to formation, in addition to corresponding propellane, of 3. The X-ray diffraction, NMR and IR studies allowed to solve the structure of molecules. It has been shown that planar nitrobenzoxazine groups are oriented to each other perpendicularly with a chair conformation of the cyclohexyl unit. The possible mechanism of reaction leading to 3 is discussed.

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Dimerization of 1,8-Diaminonaphthalene. DFT Theoretical, Ifra-red, raman and Inelastic Neutron Scattering Studies

Majerz I., Pawlukojć A., Sobczyk L., Grech E., Nowicka-Scheibe J.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 2-3

409-417

EN

Infra-red (IR), Raman (R) and inelastic neutron scattering (INS) studies were performed on solid 1,8-diaminonaphthalene. Calculations by using HF and DFT methods showed that very good reproduction of the dimeric structure found in the solid state yields the DFT method on the B3LYP/6-31G** level. The characteristic motif of dimers is an eight-membered ring with two intramolecular (highly bent) and two intermolecular N-H___Nhydrogen bridges. The four outer N-H groups remain non-bonded. This leads to a complicated pattern of vibrational spectra. No agreement between calculated and experimental (IR, R) spectra in the range of (NH2) vibrations was found.Arelatively good coincidence of experimental and theoretically predicted spectra is observed in the middle and low frequency regions, especially when analysing the INS spectra for dimeric species. The dimerization leads to a marked change in modes connected with torsional vibrations of NH2 groups.

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Wiązanie wodorowe : wybrane zagadnienia

Sobczyk L.

Wiadomości Chemiczne

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2001

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[Z] 55, 7-8

593-627

EN

In a short introduction the importance of hydrogen bonding is emphasized in life sciences and its role in molecular recognition and creation of living molecular systems. Then an attempt to define this specific molecular interaction is undertaken. Among most important features one should distinguish a particular repulsion potential which enables to approach directly interacting atoms on a distance markedly less than the sum of van der Waals radii. An important feature of hydrogen bonds is also the appearance of a double minimum potential for the proton motion. Among the main physical properties of hydrogen bonds there are analyzed dipole moments, nuclear magnetic resonance, quadrupole magnetic resonance, infra-red spectra and isotope effects. Most important isotope effects are related to infra-red spectra, geometry of bridges, phase transitions in hydrogen bonded ferroelectrics and fractionation factor. The evolution of the main characteristics is discussed depending on the acid-base properties expressed by means of the DpKa value of interacting components. A separate chapter is devoted to a dualistic nature of the interaction i.e. the structure creating and dynamical ones. The structure creating character is shown taking into account the induction of liquid crystalline properties while the dynamical properties are examplified on enzymic and photobiological processes and phase transitions in hydrogen bonded crystals. Current aspects of hydrogen bond interaction are limited to photoinduced proton transfer processes, the time resolved infra-red spectroscopy, low barrier hydrogen bonds (LBHB) and quantum molecular dynamics. In final remarks the importance of hydrogen bonding in searching for new materials of practical importance and crystal design are underlined.

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Zbigniew Malarski (1933-1998)

Sobczyk L.

Wiadomości Chemiczne

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1999

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[Z] 53, 3-4

149-164

EN

An obituary and a short review of scientific activity of Profesor Zbigniew Malarski is presented. Particularly important achievements were related to the medium effect on the associating compounds, dynamics of alcohols with large steric hindrance, the structure and spectroscopic behaviour of NHN homoconjugated cations and anions as well as geometrical correlations for OH···N hydrogen bonds. Spectacular spectroscopic and geometrical isotope effects were discovered. Full bibliography is attached.

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Pół wieku z chemią wrocławską

Sobczyk L.

Wiadomości Chemiczne

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1999

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[Z] 53, 5-6

283-304

EN

Earliest reminiscences from the post 2nd World war period, evolution and present state of the chemical educaton and research in Wrocław are presented.