Wyniki wyszukiwania - BazTech

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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.

2

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.

4

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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Phase Transitions in Guanidinium Bromoantimonate(V) {C(NH2)3]SbBr6

Jakubas R., Bator G., Ciąpała P.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 1

123-127

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Vibrational Study of the Structural Phase Transitions in a New Ferroelastic (C5H10NH2)SbCl6 Crystal by Infrared and Raman Spectroscopies

Bednarska-Bolek B., Jakubas R., Bator G., Baran J.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 2-3

385-394

EN

Infrared spectra of (C5H10NH2)SbCl6 in the region of the internal vibrations of the piperidinium cations (3500-400 cm-1) and Raman spectra in the region of internal vibrations of the SbCl6 _ anions (400-100 cm-1), around the phase transitions at Tc3 = 294 K, Tc2 = 310 K and Tc1 = 369 K, are presented and discussed. A detailed analysis has been performed for the bands assigned to the stretching and deformation vibrations of the NH2 _ and CH2 groups. It has been shown that the hydrogen bonds play an important role in the mechanism of the phase transitions and influence the dynamics of either cations or anions in different phases of (C5H10NH2)SbCl6.

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A Study on a Phase Transition in Electrodeposited Thin Film Polyaniline Using AC Conductivity Measurements

Grzeszczuk M., Bator G.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 8

1143-1150

EN

Ac conductivity - temperature dependencies of Au/polyaniline/Au structures with the electrodeposited thin film polyaniline are presented. The data for the reduced and reversibly oxidized polymer samples of estimated thickness being in 10-1-100 žm range are shown. The charge transport laws are found similar to that observed for the chemically prepared conducting polymer. The observed crossover in the conductivity - temperature dependence coincides with the increase in the electrical capacitance of the polyaniline electrode reported earlier.

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Infrared studies on the structural phase transitions in (n-C3H7NH3)2 SbBr5 and (n-C3H7NH3)3Sb2Cl9

Bator G., Jakubas R., Majerz I.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 2

314-324

EN

Internal vibration modes of(n-C3H7NH3)2SbBr5 and (n-C3H7NH3)3Sb2Cl9 were studied through their phase transitions using the infrared spectroscopy. The studies show that the vibrational states of the n-propylammonium cations change considerably during the phase transitions. The v(CC), v(CN) and v-s(NH) bands are very sensitive to the phase transition at 154 K in (n-C3H7NH3)2SbBr5, and at 232 K in (n-C3H7NH3)3Sb2Cl9. IR spectra point out the key role of the n-propylammonium cations in the phase transition mechanism of both crystals.