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- Crystal structure (6)
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- (Carboxymethyl)dimethylundecylammonium bromide (1)
- 1,3,4-Oxadiazole (1)
- 1,3,4-oxadiazole (1)
- 1,4-dipolar cycloaddition (1)
- Acetic acid (1)
Diphenyl-1,3,4-oxadiazole (DPO) crystallization experiments from solutions clearly reveal the polymorphism of the substance. Besides the formerly known centrosymmetric monoclinic structure with space group P21/c (DPO I) a new monoclinic structure with the non-centrosymmetric space group Cc is found (DPO II): a=2.4134(4) nm, b=2.4099(3) nm, c=1.2879(2) nm,?=110.048(3)°, and V=7.0363(17) nm3. The asymmetric unit contains six independent molecules in a complex packing motif. A re-determination of the crystal structure of DPO I at room temperature gives lattice parameters a=0.51885(6) nm, b=1.8078(2) nm, c=1.21435(14) nm, ?=93.193(3)°, and V=1.1373(2) nm3. X-ray measurements at 363 K show a significant increase of the unit cell volume by 1.6%. Differences between both structures concerning morphology and characteristic Raman bands are outlined in detail. DSC investigations show an irreversible transition from DPO I to DPO II at 97 °C. DPO II does not show any transition in the temperature range up to the melting point at 141 °C. The non-centrosymmetric DPO II structure shows triboluminescence.
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 ππ 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 metalorganic 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.
Three new compounds have been synthesized based on the molecular motif 2-[2,6-bis(trifluoromethyl)phenyl]-5-phenyl-1,3,4-oxadiazole, with subsequent CF3-substitution in the ortho-positions of the phenylene ring. The crystal structures of the compounds have been determined by single crystal X-ray diffraction. All compounds have a monoclinic structure. The solid state structure of the compounds is influenced by the electronic properties of the fluorine atoms, leading to the occurrence of CH...F, and CF...ϖ interactions, partly replacing ϖϖ interactions usually observed in the crystal structures of 2,5-diphenyl-1,3,4-oxadiazole derivatives. Other significant interactions than those involving fluorine appear only in rare cases. The strong impact of the fluorine atoms on the intra- and intermolecular interactions, and the molecular conformation lead to novel inputs for the understanding of molecular recognition, supramolecular assembly, and crystal packing of fluorine containing compounds.
ß-Cyclodextrin (ßCD)-formic acid (1) and ß-CDacetic acid (2) inclusion complexes crystallizeas ß-CD...0.3HCOOH...7.7H2O and ß-CD...0.4CH3COOH...7.7H2O in themonoclinic space group P21 with comparable unit cell constants. Anisotropic refinement of atomic parameters against X-ray diffractiondata with Fo 2 > 2 (Fo 2) (986/8563 and 991/8358) converged at R-factors of 0.051 and 0.054 for 1 and 2,respectively. In both complexes, the ß-CD molecularconformation, hydration pattern and crystal packing are similar,but the inclusion geometries of the guest molecules are different.The ß-CD macrocycles adopt a ``round'' conformationstabilized by intramolecular, interglucose O3(n)...O2(n + 1)hydrogen bonds and their O6H groups are systematically hydratedby water molecules. In the asymmetric unit, each complex contains one ß-CD, 0.3 formic acid (or 0.4 acetic acid), and 7.7 water moleculesthat are distributed over 9 positions. Water sites located in the ß-CD cavity hydrogen bond to the guest molecule. In thecrystal lattice, ß-CD molecules are packed in a typical ``herringbone'' fashion. In 1, the formic acid (occupancy 0.3) is entirely included in the ß-CD cavity such that its C atom is shifted from the O4-plane center to the ß-CD O6-side by 2.90 Å and C=O, C-O bonds point to this side. In 2, the acetic acid (occupancy 0.4) is completely embedded in the ß-CD cavity, in which the carboxylic C atom is displaced from the O4-plane centerto the ß-CD O6-side by 0.87 Å; the C=O bond directsto the ß-CD O6-side and makes an angle of 15°to the ß-CD molecular axis. Furthermore, bothdimethyl-ß-CD-acetic acid and ß-CD-acetic acidcomplexes form a cage structure, showing that the small guestsenclosed entirely in the cavity either in ß-CD or indimethyl--CD do not affect the packing of the host macrocycles.
The spectroscopic properties of 1-phenyl-3-benzothiazol-2-yl-5-(4-R-phenyl)-2-pyrazolines are strongly dependent on both the electronic nature of the substituent R and solvent polarity. As revealed by spectroscopic studies as a function of solvent polarity as well as temperature, for electron-rich amino donor substituents in polar solvents, deactivation of the strongly emissive charge transfer (CT) state of the basic 1-phenyl-3-benzothiazol-2-yl-2-pyrazoline chromophore has to compete with a fast intramolecular electron transfer (ET) quenching reaction. In the case of the dimethylamino derivative (R = DMA), the rate constant of ET in acetonitrile was determined to ket = 3 × 1010 s-1. This ET process can be utilized for metal ion sensing by introducing nitrogen containing aza crown ether receptor units to the 4-position of the 5-phenyl group. The spectroscopically determined ET rates of the 5-(N-alkyl)anilino substituents, a DMA, a tetrathia- (AT415C5), and a tetraoxa-monoaza-15-crown-5 (A15C5) group, correlate with electrochemical data and increase in the order AT415C5 < A15C5 < DMA. The metal ion sensing abilities of the two crowned derivatives are presented, and the different signaling mechanisms include binding to the crown ether in the 4-R-position, chelate formation in the 3-benzothiazol-2-yl-2-pyrazoline moiety, and electrophotochemical detection. Furthermore, the rigid "pseudo spiro" geometry of the molecules, which holds the three substituents of the central 2-pyrazoline ring in a fixed prearrangement, was confirmed by X-ray structure analysis.
For the fluorescent ligand 1-(9-anthrylcarbonyl)-3,3-tetramethylenethiourea with Cu(ClO4)2 or strong acids an unusual rearrangement reaction occurred yielding a highly emissive S-(9-anthryl)isothiouronium salt. This rearrangement product was characterised by NMR spectroscopy and X-ray analysis as well as absorption and fluorescence spectroscopy. Additionally, the chemical and complexation behaviour of the N-anthrylcarbonylthiourea derivative is compared to that of its naphthyl and phenyl analogues.
A procedure has been developed for the synthesis of N-cyclopentadienyl amidinium ylides of the general formula C5(CO2Me)4[ArNC(Ar')NHAr]. According to the X-ray diffraction data, 1H and 13C NMR spectroscopy, and MNDO quantum-chemical calculations, the title compounds have a zwitterionic structure with the positive charge localized over the amidine NÄCÄN triad, and the negative charge, over the cyclopentadiene fragment. The configuration of the amidine moiety is stabilized by additional interaction of the NH hydrogen atom with the negatively charged cyclopentadiene ring (-bonding). The ylides are chiral due to atropoisomerism arising from a high energy barrier (G 298 >25 kcal/mol) to rotation of the Ar' substituent about the ordinary CÄC bond in the amidinium fragment.
Indolizines, known as a useful class of fluorophores, were bridged yielding biindolizines. We intended to obtain long wavelength absorbing and emitting fluorescent systems suitable for fluorescence labeling of biomolecules. The influence of the different kinds of coupling on the absorption and fluorescence behaviour of the resulting biidolizines was studied. The new fluorophore systems were characterized spectroscopically by their absorption and emission maxima and their quantum yields.
A bisamidopyridine-type receptor, N,N'-bis(6-methyl-2-pyridyl)pyridine-2,6-dicarboxamide (1), and its CoIII complex were prepared and their X-ray structures were compared to those of N,N'-diphenylpyridine-2,6-dicarboxamide (2) and CoIII(2)2. Introduction of the two additional coordinative groups resulted in second-order interactions between the central ion and the nitrogen atoms of the terminal pyridine moieties in the crystalline state. Solution studies in acetonitrile revealed the importance of these interactions for the ligand's metal ion recognition ability. Whereas 2 only binds to PbII and CuII, 1 yields complexes with a majority of the heavy and transition metal ions studied, CoII, NiII, CuII, ZnII, FeIII, FeII, HgII, and PbII, respectively. The cation binding properties in solution were investigated by absorption spectroscopy and in the case of 1-MII/III, the formation of two spectroscopically distinguishable types of complexes was found. Protonation experiments and theoretical considerations helped to gain further insight into possible modes of coordination in solution.
Aza-enamines X - Formylation of Pyrazole-4-carbaldehyde Hydrazones at the Hydrazonoazomethine C-Atom
(2003)
1,3-Disubstituted 1H-pyrazole-4-carbaldehyde-N,N-dimethylhydrazones 1 reacted with the Vilsmeier-Haackreagent, corresponding to the aza-enamine concept, in an electrophilicsubstitution reaction at the azomethine C-atom yielding the 1,4,5-triaza-pentadieniumsalts 2. These were hydrolysed to give2-hydrazono-2-(1H-pyrazole-4-yl)ethanals 3. The electrophilic attack did not takeplace at the vinylogous position 5' of the pyrazoles.