Structure and Spectroscopic Behaviour of Adduct of 2,6-dichloro-4-nitrophenol with 2,4,6-trimethylpyridine

2,4,6-trimethylpyridinium 2,6-dichloro-4-nitrophenolate crystallizes in monoclinic system, space group Ρ2$\text{}_{1}$/c, a = 7.534(2), b = 26.673(5), c = 8.452(2) Å, β = 116.16(3)°, Z = 4. The planar molecules are arranged in the lattice as antiparallel oriented pairs with the symmetry centre. The O$\text{}^{-}$···Η-Ν$\text{}^{+}$ hydrogen bonds are relatively long, 2.686(4) Å. The C-O bond length, 1.250(4) A, indicates an extended charge separation. The IR and UV-VIS spectra in KBr pellets confirm the ion pairs to be present in the solid state

p-N,N′-tetraacetylodiaminodurene. The structure and vibrational spectra

The crystal and molecular structure of p-N,N′-tetraacetylodiaminodurene (TADD) is reported based on the X-ray diffraction studies. The N-acetyl moieties are planar and all N-acetyl groups are perpendicular to the ring plane. Methyl groups both of acetyl moieties and of durene form a number of non-conventional hydrogen bonds with nitrogen and oxygen atoms. The vibrational spectra very well reflect the structure of molecules and their contacts. They are compared with calculated data by using various theoretical approaches. The neutron scattering spectra show two tunnel lines of low energy values (at ±0.9 and ±2.3 μeV at 4 K), which can be ascribed to methyl groups of N-acetyl moieties, which behave more freely than those attached to the phenyl ring

4,4'-, 5,5'- and 6,6' -dimethyl-2,2'-bipyridyls: the structures, phase transitions, vibrations and methyl group tunneling of their complexes with chloranilic acid

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

X-ray diffraction and inelastic neutron scattering study of 2,6-dimethylpyrazine chloranilic acid complex

The DMP (.) CLA and DMP (.) CLA-d(2) crystals below 100 K are monoclinic, space group P2(1)/c with four molecules in the unit cells. Infinite chains of hydrogen bonded counterparts are formed with 0(...)N distances equal to 2.767(2) and 2.639(2) for non-deuterated DMP (.) CLA. Deuteration leads to the Ubbelohlde effect particularly well manifested in the second short O-(HN)-N-... bridge (elongation by ca. 0.02 angstrom). In the IR spectra a Hadzi's trio of the broad absorption is observed characteristic of strong hydrogen bonds. In the INS spectra the vibrational density of states and methyl rotational tunnel splittings were determined. The temperature dependence of tunneling bands enabled to make mode assignments and to determine the methyl rotational potentials. Comparison of the results to the pure electron donor DMP was made and the difference found can be almost completely assigned to the steric changes of the environment. A weak isotope effect with deuteration of the (OHN)-N-... bridges of the DMP (.) CLA complex is assigned to a charge transfer of bel e = 0.006. (c) 2006 Elsevier B.V. All rights reserved

Crystal structural analysis of methyl-substituted pyrazines with anilic acids: a combined diffraction, inelastic neutron scattering, 1 H-NMR study and theoretical approach

The crystal and molecular structures of (1) 2-methylpyrazine (2MP) with 2,5-dichloro-3,6-dihydroxy-p-quinone (chloranilic acid, CLA), (2) 2-methylpyrazine (2MP) with 2,5-dibromo-3,6-dihydroxy-p-quinone (bromanilic acid, BRA), (3) 2,3,5-trimethylpyrazine (TrMP) with 2,5-dichloro-3,6-dihydroxy-p-quinone (chloranilic acid, CLA), and (4) 2,3,5-trimethylpyrazine (TrMP) with 2,5-dibromo-3,6-dihydroxy-p-quinone (bromanilic acid, BRA) were analyzed in terms of the number of independent methyl groups in their crystal structure. The inelastic neutron back-scattering spectra at low temperature (4–40 K) were discussed in terms of methyl group tunnelling. The INS spectra were compared with the temperature dependence of the 1H-NMR spin–lattice relaxation time, particularly at low temperatures, where CH3 tunnelling is postulated. The infrared and Raman spectra at room temperature were recorded for all complexes under investigation. Furthermore, the vibrational spectra were discussed in terms of the structure of molecules and their interactions. The structural phase transition of the TrMP·CLA complex at 171/175 K (cooling/heating) was characterized by DSC and single-crystal X-ray diffraction. Full-geometry optimization was carried out in the solid state in order to obtain the minimum structures and bonding properties. The results are in very good agreement with the experimental data. The infrared spectrum in the harmonic approximation was calculated and a comparative vibrational analysis was performed. CRYSTAL09 vibrational results appear to be in good agreement with the experimental result

Structure and tunneling splitting spectra of methyl groups of tetramethylpyrazine in complexes with chloranilic and bromanilic acids

The crystal and molecular structure of the 2,3,5,6-tetramethylpyrazine (TMP) complex with 2,5-dibromo-3,6-dihydroxy-p-quinone (bromanilic acid, BRA) has been studied and the results are compared with TMP CLA (2,5-dichloro-3,6- dihydroxy-p-quinone (chloranilic acid, CLA) complex. The X-ray structure of TMP BRA complex indicates the formation of dimeric units, in which two BRA - anions are connected by two O-H···O (2.646(2) Å) hydrogen bonds, whereas the cations and anions are joined together by strong N+-H···O- (2.657(2) Å) hydrogen bonds. The results are analyzed in terms of both the methyl group surroundings and the C-H···O and N+- H···O- (or N···H-O) bridge formations. Both effects, the strength of the N+- H···O- hydrogen bonds and steric hindrance for the rotations, are responsible for the CH3 group dynamics. For the TMP CLA and TMP BRA complexes, the inelastic neutron backscattering spectra were also investigated. In the case of TMP CLA, four tunneling signals have been observed in the energy range ±30 ÎeV, which indicates four inequivalent methyl groups in the crystal structure at the lowest temperature. No tunneling splitting is observed in the case of the TMP BRA complex, most probably due to the overlapping with the elastic peak. The tunneling results are consistent with the 1H NMR spin-lattice relaxation time investigations in a wide temperature range, which also point to the CH 3 group tunneling effect in the case of TMP CLA. © 2014 American Chemical Society

The (2:1) complex of picric acid with tetramethylpyrazine. The structure,l IR spectra and tunnel splitting of methyl groups

The crystal structure of 2:1 picric acid (PAH) with tetramethylpyrazine (TMP) was determined by using X-ray diffraction studies. Two equivalent N+-H center dot center dot center dot O- hydrogen bonds are formed with the length of 2.601 angstrom (calculated 2.640 angstrom). In the IR spectra very broad doublet at ca. 2000 and 2400 cm(-1) is observed, which can be interpreted as due to symmetric and asymmetric N+-H vibrations. In neutron backscattering 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 mu eV. (C) 2010 Elsevier B.V. All rights reserved