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ABSTRACT: The almost planar molecular complex, formed by 3,4,7,8-tetramethyl-phenantroline (Me 4 phen) and pic-ric acid (2,4,6-trinitrophenol, PA), has been investigated by using X-ray diffraction, vibrational spectros-copy, tunnel splitting and theoretical analysis. In the crystal of Me 4 phenÁPA two short bifurcated hydrogen bonds N + –HÁÁÁO À [2.6238(14) Å] and N + –HÁÁÁN [2.6898(15) Å] are created. Infra-red spectra show the hydrogen bonds are short. The neutron backscattering spectrum of Me 4 phenÁPA at 3 K shows two tunneling peaks at ca. 1 and 3 leV. The number of the peaks is consistent with X-ray diffraction stud-ies, which disclosed the inequivalence of methyl groups in the crystal structure. The comparison of the tunnel splitting for neat Me 4 phen and for its complex with picric acid indicates that in the latter case the methyl groups are more strongly engaged in the intermolecular interactions, particularly with nitro group oxygen atoms of picric acid, leading to an increase of the CH 3 rotational barrier height.
Chemical Physics 01/2013; · 1.90 Impact Factor
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ABSTRACT: In crystalline state 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) forms with 4,4 0 -di-t-butyl-2,2 0 -bipyridyl (dtBBP) the hydrogen bonded chains along the b-axis. From one side of the CLA molecule the proton transfer takes place and the hydrogen bond length is very short (2.615 Å). A contin-uous infrared absorption is observed for dtBBPÁCLA in the wavenumber range between 3100 and 800 cm À1 also indicating the strong hydrogen bonds. The DSC measurements show a weak, close to con-tinuous, phase transition at 414 K. The complex dielectric permittivity for a single crystal sample was measured in the temperature range 100–440 K and at frequencies between 200 Hz and 2 MHz. The dielectric response is a combination of semiconducting properties and a relaxation process most probably connected with the proton dynamics in the hydrogen bonds. The mechanism of the structural phase tran-sition is discussed.
Chemical Physics 01/2012; 392:114-121. · 1.90 Impact Factor
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ABSTRACT: The crystal and molecular structures of 4,4(')- and 6,6(')-dimethyl-2,2(')-bipyridyl complexes with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) have been determined and compared with those of the complex with the 5,5(')-derivative, which is known to possess interesting antiferroelectric properties. In the crystalline state, all three compounds form hydrogen bonded chains with N(+)-H···O(-) and O-H···N bridges on both sides of the bipyridyl constituent. The comparison of three derivatives indicates that the N(+)-H···O(-) hydrogen bonds are shortest for the 5,5(')-dimethyl complex. The 4,4(')- and 6,6(')-derivatives do not show any ferroelectric feature. The 6,6(')-one is, however, characterized by a continuous phase transition, revealed in the differential scanning calorimetry, dilatometric, and dielectric characteristics. The tunneling splitting measured by neutron backscattering in the energy range ±30 μeV for the neat dimethyl bipyridyls and their complexes with CLA indicates that the different splittings are primarily due to the crystal packing effect and that charge transfer between interacting compounds plays only a minor role.
The Journal of chemical physics 07/2011; 135(4):044509. · 3.09 Impact Factor
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ABSTRACT: The complexation of 2,5-dimethylpyrazine (2,5-DMP) with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (CLA) leads to the formation of the hydrogen bonded OH⋯N infinite chains without any proton transfer. In the high and medium frequency region of the IR spectra a characteristic Hadži’s trio with maxima at ca. 2400, 1800 and 1150 cm−1 is observed. The infrared, Raman and inelastic neutron scattering (INS) spectra are compared with those calculated by using the DFT methods applied to the crystalline state. The optimization of the structure by using this theoretical approach is also performed. Very good conformity of the experimental and theoretical structures is visible. The reproduction of vibrational spectra is also good except for the low frequency bands related to the CH3 torsional modes. One gets relatively good agreement by using PWC(dnp) approach. Applications of other theoretical models leads to much higher values of CH3 torsional frequency.Graphical abstractThe infrared, Raman and inelastic neutron scattering (INS) spectra of 2,5-DMP with CLA, its crystal structure, the DFT method applied to the crystalline state, the hydrogen bonded OH⋯N infinite chains without any proton transfer.Research highlights► A novel complex of 2,5-dimethylpyrazine with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone. ► The crystal structure at 100 K is presented. ► The infrared, Raman and inelastic neutron scattering spectra are shown. ► They are compared with calculated by using the DFT methods applied to the crystalline state. ► The calculated structure and the frequencies are well consistent, except of the CH3 torsional mode.
Chemical Physics. 05/2011; 380:34-39.
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ABSTRACT: The crystal structure of 2:1 picric acid (PAH) with tetramethylpyrazine (TMP) was determined by using X-ray diffraction studies. Two equivalent + NAHÁ Á ÁO À hydrogen bonds are formed with the length of 2.601 Å (calculated 2.640 Å). In the IR spectra very broad doublet at ca. 2000 and 2400 cm À1 is observed, which can be interpreted as due to symmetric and asymmetric + NAH vibrations. In neutron backscatter-ing two tunnel splittings are observed, in agreement with the symmetry of 2:1 assemblies. At 4 K the tunnel peaks are located at 3.17 and 4.24 leV.
Journal of Molecular Structure 01/2010; 975:298-302. · 1.63 Impact Factor
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ABSTRACT: The complexes formed by squaric acid with 4,4 0 -and 5,5 0 -dimethyl-2,2 0 -bipyridine were prepared (abbre-viation 4-DMBPH + ÁHSQ À and 5-DMBPH + ÁHSQ À ÁH 2 O, respectively). Their crystal structure shows that ion-ization of squaric acid leads to formation of dimeric double ionized (HSQ) 2 À2 units and monoprotonated bipyridines. The N + AH groups form bifurcated hydrogen bonds with the C@O group of squarate anion and with the second non-protonated nitrogen atom. In the case of 5,5 0 -DMBP the complex crystallizes with one water molecule attached to the charged N + AH group, with OH groups forming hydrogen bonds to carbonyl groups of squaric acid. Infrared and Raman spectra reflect sufficiently well the packing. Most spectacular is the continuous absorption ascribed to the (HSQ) 2 À2 units with two very short OHÁ Á ÁO hydrogen bonds. The analysis has been performed for the 4-DMBPH + ÁHSQ À complex by comparison of the experimental infrared spectra with the calculated ones for separated ions and the crystalline state.
Journal of Molecular Structure 01/2010; 976:30-35. · 1.63 Impact Factor
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ABSTRACT: The inelastic neutron scattering (INS), infrared and Raman spectra of crystalline 2,6-dimethylpyrazine (26DMP) and its complex with chloranilic acid (26DMP·CLA) were measured. Simultaneously the DFT calculations of the molecular structures and frequencies of the normal vibrations were performed by using various functionals. The INS spectra were simulated in the energy range up to 1200 cm−1, on the basis of the calculated frequencies. A very good conformity was obtained between experimental and calculated data with respect to the structure as well as to frequencies, with exception, however, of the CH3 torsional modes. The structural analysis based on the deviation from the sum of the van der Waals radii showed that the packing of the methyl groups in the 26DMP·CLA complex was markedly stronger than that in the neat 26DMP. However, the DFT calculations overestimated the role of this effect that may be due to a limitation of the applied methods. In addition the anharmonicity of the rotational potential led to the librational energies different from those obtained using a harmonic potential.
Journal of Molecular Structure. 05/2008; 892:261-267.
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ABSTRACT: The infrared and Raman spectra for durene, tetracyanobenzene and their 1 : 1 complex were studied. Simultaneously the neutron scattering experiments (INS and QENS) were performed. A detailed analysis of the modes assigned to the methyl groups vibrations were analyzed based on the simulated frequencies and intensities by using the GAUSSIAN-03 and auntie-CLIMAX programs. A good agreement between calculated frequencies and INS experimental ones was found. Moreover the calculations generate, with a quite high accuracy, the observed lattice phonons below 70 cm−1. The QENS studies have shown that the activation energy for the 120° CH3 jumps equal to 49 ± 13 meV for durene and 35 ± 12 meV for the complex confirming that the complexation leads to a decrease of the potential barrier for the methyl group rotations.
Phase Transitions 06/2007; 80(Nos. 6-7):489-500. · 1.01 Impact Factor
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ABSTRACT: Elastic and inelastic neutron scattering as well as IR spectroscopic and DFT theoretical studies on tetramethylpyrazine (TMP)–1,2,4,5-tetracyanobenzene (TCNB) complex have shown that decisive in crystal packing are C–H⋯N hydrogen bonds, although in the H-bonding scale they should be treated as rather weak. In contrast to the other charge transfer (CT) complexes, like this in TCNB–durene, there is no alternation of molecules in stacking. INS spectra have shown a marked decrease of the CH3 torsional frequencies that can be discussed in terms of the charge transfer from TMP toward TCNB counterpart. The role of such a phenomenon was confirmed by calculations of frequencies for ionized molecule of TMP which show a giant effect of ionization on the rotational potential of CH3 groups. Theoretical analyses of various orientations of interacting molecules have shown that a deepest energy minimum is reached for perpendicular arrangement with C–H⋯N hydrogen bonding of the H⋯N distance equal to 2.31 Å (experimental value 2.37 Å).
Chemical Physics 05/2006; 327:237-246. · 1.90 Impact Factor
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ABSTRACT: The results of inelastic neutron scattering (INS), Raman and infrared (IR) studies on 1,2,4,5-tetramethylbenzene (durene), tetramethylpyrazine (TMP) and tetramethyl-1,4-benzoquinone (TMBQ) in the solid state are reported. The observed frequencies are analyzed on the basis of DFT calculations. The low frequency region, below 400 cm(-1), related to the torsional and bending out-of-plane vibrations of the CH(3) groups, is of particular interest. The detailed analysis is possible due to the simulation of the INS spectra by using the auntie-CLIMAX program. It is shown that the observed low frequency INS bands are dramatically shifted, compared to the calculated ones, towards higher frequencies. Although one cannot exclude deficiencies of theoretical methods as applied to low frequency modes, it seems more probable the interpretation based on an existence of non-conventional CH(...)pi, CH(...)N, CH(...)O hydrogen bonds formed by the methyl groups in crystalline phases.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 04/2006; 63(3):766-73. · 2.10 Impact Factor
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ABSTRACT: The structure of the 2:1 hexamethylbenzene (HMB)–tetracyanoethylene (TCNE) complex was determined at 100 K. In the crystalline lattice the molecules of HMB (D) and TCNE (A) are arranged in DDADDADD stacks along the b-axis. Based on the red shift of the m(C"N) IR frequencies the charge transfer (CT) degree (Z) was estimated to be equal to 0.14. It is markedly higher than that for the complex of HMB with tetracyanoquinodimethane (TCNQ) for which Z = 0.06. The analysis of vibrational modes connected with torsional motion in the low frequency region was performed based on the inelastic neutron scattering (INS) experiments and DFT theoretical calculations. The correlation between m exp /m calc and m calc shows a deviation of experimental values from calculated ones. It is the higher the lower is the frequency of the analysed mode. The comparison of correlations for neat HMB and its complexes with TCNQ and TCNE suggests that some role in decreasing the barrier to rotation can be played by the charge transfer between D and A molecules. Ó 2006 Published by Elsevier B.V.
Chemical Physics 01/2006; 327:311-318. · 1.90 Impact Factor
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ABSTRACT: Inelastic incoherent neutron scattering (IINS) spectra were obtained at 10K for normal and deuterated l-cysteine. Raman and infrared spectra were also recorded. Geometry of l-cysteine molecule was optimized for the zwitterion form using ab initio HF/6-31G* level. The theoretical frequencies of normal and d(4)-l-cysteine were compared with INS, Raman and IR spectra. Normal coordinate analysis and band assignments based on ab initio calculations and experimental data are presented.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 10/2005; 61(11-12):2474-81. · 2.10 Impact Factor
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W Sawka-Dobrowolska,
G Bator,
L Sobczyk,
A Pawlukojc,
H. Ptasiewicz-Bak,
H. Rundloef,
P. Jagielski,
J. A. JANIK,
J. KRAWCZYK,
M. Nowina-Konopka,
O. Steinsvoll,
E Grech, J Nowicka-Scheibe,
M Prager
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ABSTRACT: Elastic, quasielastic, and inelastic neutron-scattering studies on the
charge-transfer hexamethylbenzene-tetracyanoquinodimethane complex
The Journal of Chemical Physics 05/2005; 123:124305. · 3.33 Impact Factor
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ABSTRACT: In searching for new molecular materials the crystals of 1:1 complexes of tetramethylpyrazine (TMP) with chloranilic acid (CLA) were grown. In the crystalline lattice of TMP.CLA infinite chains of hydrogen bonded components are formed. Very strong (d (O···N) = 2.692(2 A) hydrogen bonds without proton transfer are present. The components of the complex form stacks of parallel arrangement with the distance typical of van der Waals interaction. One can conclude that in packing, interactions via hydrogen bonds play a decisive role. In the IR spectrum one observes a broad, continuous absorption with well resolved trio typical of strong hydrogen bonds. A detailed analysis of IR and Raman spectra in the low frequency region related to deformation vibrations of CH 3 groups shows that strong interaction via hydrogen bonding only slightly affects the dynamics of these groups.
Structural Chemistry 01/2005; 16(3):281-286. · 1.85 Impact Factor
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ABSTRACT: The vibrational spectra of chloranilic acid (2,5-dihydroxy-3,6-dichloro-[1,4]-benzoquinone) in the solid state were studied by using inelastic neutron scattering (INS), infrared (IR) and Raman (R) spectroscopy. The spectra were compared with simulated spectra using the Gaussian and Climax programs. Sufficiently good agreement between the experimental and theoretical (DFT) spectra is observed although the calculations show that in the crystalline state a bifurcation of hydrogen bonds takes place. Relatively strong intermolecular interactions are noticeable when the experimental (x-ray) and calculated bond lengths and angles with participation of OH groups are compared. The studies of the deuterium isotope effect in the IR and R spectra enabled us to analyse the low-frequency out-of-plane vibrations and particularly the ν(OH) and ν(OD) modes. In the case of the ν(OH) and ν(OD) vibrations, one observes a strong asymmetry of the bands (low-frequency wings), which can be interpreted in terms of a coupling of the ν(OH) mode with low-frequency ones damped by the lattice phonons and no fine structure of the ν(OH) and ν(OD) bands is observed. Copyright © 2003 John Wiley & Sons, Ltd.
Journal of Physical Organic Chemistry 09/2003; 16(10):709 - 714. · 1.96 Impact Factor
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ABSTRACT: Inelastic neutron scattering (INS) spectra of solid 2,5-dihydroxy-1,4-benzoquinone were measured and compared with IR and Raman data. The INS spectrum is very well reproduced in the region below 1000 cm(-1) by DFT calculations on the B3LYP/6-311++G** level using Gaussian and Climax programs. To get a better agreement one should take into account additional interactions of OH groups in the solid state leading to an increase of the gamma(OH) frequency and to a decrease of frequencies for modes in which the delta(OH) participates. The studies of the deuterated compound in IR enabled to correct the assignment of gamma(OH) vibrations. Highly asymmetric nu(OH) band observed in IR spectrum with sharp maximum at about 3300 cm(-1) is discussed in terms of a stochastic approach to the analysis of hydrogen bonded systems.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 03/2003; 59(3):537-42. · 2.10 Impact Factor
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ABSTRACT: The structure of the complex of 1,8-bis(dimethylamino)naphthalene with 1,8-bis(4-toluenesulphonamido)-2,4,5,7-tetranitronaphthalene (DMAN TSATNN) has been determined by X-ray diffraction methods. To the best of the authors' knowledge this is the first structure found to contain the [NH⋯N]+ and [NH⋯N]− hydrogen bonds. The crystals are triclinic, space group P, with a=13.03(1), b=12.10(1), c=13.99(1) Å, α=109.86(7), β=104.04(7), γ=92.26(6)° and Z=2. The structure solved by the direct methods has been refined to R=0.049 for 3281 non-zero reflections. The [NH⋯N]+ and [NH⋯N]− bridges of 2.610(5) Å with ∠ NHN = 152(5)° and 2.600(5) Å with ∠ NHN = 153(5)° are characterized by an asymmetric and strongly asymmetric proton distribution, respectively. The IR protonic absorption is located in two different regions at about 500 and 2700 cm−1 for the [NH⋯N]+ and [NH⋯N]− hydrogen bonds respectively.
Journal of Molecular Structure.
