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- 1,3,4-oxadiazole (1)
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- Diphenyl-1,3,4-oxadiazole (1)
- Diphenyl-oxadiazoles (1)
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Crystal structures of four different di-aryl-1,3,4-oxadiazole compounds (aryl = 2-pyridyl-, 3-pyridyl-, 2-aminophenyl-, 3-aminophenyl-) are determined. Crystallization of di(2-pyridyl)-1,3,4-oxadiazole yielded monoclinic and triclinic polymorphs. The structures are characterized by the occurrence of pi-pi interactions. Additionally, in case of the aminophenyl compounds intra- as well as intermolecular hydrogen bonds are found that influence the packing motif as well. Since these molecules are often used as ligands in metal-organic complexes similarities and differences of the molecular conformation between the molecules in the pure crystals and that of the ligands in the complexes are discussed. (c) 2006 Elsevier B.V. All rights reserved.
Structural and spectroscopical study of a 2,5-diphenyl-1,3,4-oxadiazole polymorph under compression
(2006)
The x-ray pattern and the Raman and luminescence spectra of crystalline 2,5-diphenyl-1,3,4-oxadiazole in one of its polymorphic forms (DPO II) have been investigated under pressure up to 5 GPa. The behaviour of the lattice parameters under compression was determined and it was found that the Murnaghan equation of state provides a good description of the volume-pressure relationship of DPO II. The values for the bulk modulus and its pressure derivative are K-0 = 8.6 GPa and K-0' = 7.2. The analysis of the Raman spectrum under compression clearly shows the pressure- induced shift of the Raman modes to higher frequencies. The mode Gruneisen parameters for the lattice modes were determined. Additionally, it was found that the emission spectrum of DPO II moves to lower energies and that the luminescence intensity decreases when pressure is applied
The formation of different micro- and nanostructures during the chemical synthesis of polypyrrole is reviewed shortly based on the conceptions of hard- and soft-templating models. Contrary to other models that emphasize the role of micelles it is found here that during the oxidative polymerization of pyrole using sulfonic acid dopants a crystalline hard template is found in the first steps of the reaction before the addition of the oxidant. This template is formed by a complex consisting of 2,5-bis(pyrrole-2-yl)pyrrolidine and the sulfonic acid anion. The acid catalyzed formation of this specific tripyrrole is discussed. (C) 2009 Elsevier B.V. All rights reserved.
The crystalline structures of two modifications of a compound containing the oxadiazole ring, 2,5-di-(4- aminophenyl)-1,3,4-oxadiazole (DAPO) were determined. One of these modifications contains water molecules in the crystal structure, which is observed for the first time for an oxadiazole crystal. Both crystals show an orthorhombic structure. The water free modification, DAPO L belongs to the space group Pbca (61) and has the lattice parameters: a = 13.461(5), b = 7.937(3) and c = 22.816(8) angstrom (CCDC 246608). The water containing pseudo-polymorph, DAPO 11, has the space group Cmcm (63) and the lattice parameters: a = 16.330(5), b = 12.307(2) and c = 6.9978(14) angstrom (CCDC 246609). To gain information on the inter molecular interactions within the crystals, X-ray experiments under compression at ambient temperature and under heating at vacuum conditions were performed. Neither DAPO I nor DAPO II undergo phase transitions in the ressure range up to 5 GPa, as could be concluded from X-ray and Raman experiments. X-ray and calorimetric studies indicate that DAPO II dehydrates into DAPO I under increasing temperature. Structural considerations suggest a two-stage process. The compression behavior of both substances is well described by the Murnaghan equation of state (MEOS) and the values of the bulk modulus and its pressure derivative are determined for these crystals. Additionally, in the case of DAPO I, also the thermal expansion coefficient an was measured. (c) 2005 Elsevier Ltd. All rights reserved
Results are presented from structural and high-pressure investigations on four differently but symmetrically fluorine substituted 2,5di(phenyl)-1,3,4-oxadiazoles. The substitution pattern includes the para-, meta-, or ortho- substitution and the fully fluorinated 2,5-bis(pentafluorophenyl)-1,3,4-oxadiazole. The crystal structure depends on the molecular structure and results in a different high-pressure behavior. Parameters for the Murnaghan equation of state (EOS) are determined for every compound and the anisotropic pressure response of the crystal lattice is discussed. Although the EOS parameters, bulk modulus K. and its pressure derivative K'(o) are of the same order of magnitude for all four compounds, the anisotropy of strain is noticeably different. (c) 2005 Elsevier B.V. All rights reserved
The molecular structure of poly(p-phenylene-1,3,4-oxadiazole) (POD) is investigated using i.r. and Raman spectroscopy. Both methods reveal characteristic differences for the a- and b-POD forms that are most obvious in the spectral region between 1500 and 1650 cm-1. The spectra for dimer and tetramer compounds already show the same features as found for longer chains. Based on molecular modelling calculations these differences are assigned to cis and trans conformations of the main chain segments. High pressure measurements show a linear shift of the Raman lines and support the result of the thermodynamic stability of the trans conformation.
Aspects of morphology control during the oxidative synthesis of electrically conducting polymers
(2009)
The formation of micro- and nanostructures during the oxidative polymerization of polypyrrole and polyaniline is investigated using different sulfonic acid dopants. Rod- or tube-like structures are found in polypyrrole as well as in polyaniline without addition of further compounds to the initial reaction mixture of monomer, dopant and oxidant. In these cases, always a crystalline precursor complex composed of a dopand molecule and the pure monomer (aniline) or a trimeric moiety (pyrrole) serves as in-situ template. In most cases the surface of the growing polymer is covered by secondary structures with much smaller sizes so that a hierarchical order of structures at different length scales results. Corresponding model considerations for the polymerization process are outlined. Additionally, unusual structures like platelets, frames, rings, or ribbons are observed in the polypyrrole synthesis in the presence of fluorosurfactants.
Results of a high pressure x-ray study of 2,5-di(4-pyridyl)-1,3,4-oxadiazole up to 2.5 GPa are presented and discussed. Parameters for the Murnaghan equation of state are derived. The bulk modulus amounts to K-0 = 4.6 +/- 0.3 GPa and its pressure derivative to K-0' = 7.4 +/- 0.6. These values are comparable to values of other diphenyl-1,3,4- oxadiazoles. The anisotropy of the compression is analysed using the strain tensor and discussed based on the anisotropy of the intermolecular interactions