Norwid-Rasmus Behrnd

Synthesis and crystal engineering of fluorinated stilbenes

Three new polyfluorinated (E)-4-(4-bromostyryl)benzonitriles were obtained by the Horner–Wadsworth–Emmons approach to investigate intermolecular interactions in the crystalline state and the formation of co-crystals. Electrostatic surface potentials and dipole moments were calculated by ab initio methods. Three types of main intermolecular interactions were addressed to be used as a driving force to form polar co-crystals: CN⋯Br interactions lead to chain formation. Stacking of F-aromatic and H-aromatic rings is present. C–F⋯H and C–F⋯F interactions were identified, which are weak driving forces to align molecules sidewise. Crystal structures of the three stilbenes are centric. By formation of solid solutions [(E)-4-(4-bromostyryl)-2,3,5,6-tetrafluorobenzonitrile]x·[(E)-4-(4-bromo-2,3,5,6-tetrafluorostyryl)benzonitrile]1−x, polar properties were observed. In the case of (E)-4-(4-bromostyryl)benzonitrile·(E)-4-(4-bromo-2,3,5,6-tetrafluorostyryl)-2,3,5,6-tetrafluorobenzonitrile, a non-polar 1 ∶ 1 ordered structure is formed.

Influence of the solvent of crystallization on the orientational disorder of (trans)-4-chloro-4′-nitrostilbene

The polar molecule (trans)-4-chloro-4′-nitrostilbene, which shows significant second harmonic generation in the solid state, has been crystallized from 12 different solvents. Careful X-ray diffraction studies on 18 different crystals revealed varying deviations from an exact 50 : 50 head-to-tail orientational disorder and thus from the centrosymmetric average structure reported previously. The degree of disorder varies somewhat with the solvents used for crystallization. A weak correlation is found between the deviations from a centrosymmetric structure and the polarity of the solvent. No polymorphs were observed.

Polarity formation in molecular crystals studied by scanning pyroelectric microscopy

Scanning pyroelectric microscopy (SPEM) has successfully been applied to study spatial polarisation distributions in channel-type inclusion crystals and zeolite based host-guest systems, which show macroscopic polarity as the result of polar growth or oriented sorption of hyperpolarisable molecules.