Peculiar orientational disorder in 4-bromo-4'-nitrobiphenyl (BNBP) and 4-bromo-4'cyanobiphenyl (BCNBP) leading to bipolar crystals
| Autor: | Hanane Aboulfadl, Ravish Sankolli, Matthias Burgener, Jürg Hulliger, Michel Bonin, Gaël Labat, Martin Sommer, Michael Wübbenhorst |
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| Rok vydání: | 2016 |
| Předmět: |
Diffraction
endocrine system Polarity (physics) 02 engineering and technology 010402 general chemistry 01 natural sciences Biochemistry Crystal bipolar crystals Microscopy 540 Chemistry General Materials Science heterocyclic compounds Symmetry breaking Crystallography Chemistry organic chemicals General Chemistry 021001 nanoscience & nanotechnology Condensed Matter Physics orientational disorder Acceptor Research Papers humanities 3. Good health 0104 chemical sciences Pyroelectricity QD901-999 Chemical physics Polar 570 Life sciences biology bacteria structural defects 0210 nano-technology |
| Zdroj: | IUCr Journals IUCrJ Burgener, Matthias; Oulevey, Hanane; Labat, Gaël Charles; Bonin, Michel; Sommer, Martin; Sankolli, Ravish; Wübbenhorst, Michael; Hulliger, Jürg (2016). Peculiar orientational disorder in 4-bromo-4′-nitrobiphenyl (BNBP) and 4-bromo-4′-cyanobiphenyl (BCNBP) leading to bipolar crystals. IUCrJ, 3(3), pp. 219-225. International Union of Crystallography 10.1107/S2052252516006709 IUCrJ, Vol 3, Iss 3, Pp 219-225 (2016) |
| DOI: | 10.1107/S2052252516006709 |
| Popis: | Two dipolar biphenyls show significant 180° orientational disorder resulting in bipolar as-grown crystals. An added symmetrical biphenyl interferes with polarity formation and inverts the initial bipolar state. 180° orientational disorder of molecular building blocks can lead to a peculiar spatial distribution of polar properties in molecular crystals. Here we present two examples [4-bromo-4′-nitrobiphenyl (BNBP) and 4-bromo-4′-cyanobiphenyl (BCNBP)] which develop into a bipolar final growth state. This means orientational disorder taking place at the crystal/nutrient interface produces domains of opposite average polarity for as-grown crystals. The spatial inhomogeneous distribution of polarity was investigated by scanning pyroelectric microscopy (SPEM), phase-sensitive second harmonic microscopy (PS-SHM) and selected volume X-ray diffraction (SVXD). As a result, the acceptor groups (NO2 or CN) are predominantly present at crystal surfaces. However, the stochastic process of polarity formation can be influenced by adding a symmetrical biphenyl to a growing system. For this case, Monte Carlo simulations predict an inverted net polarity compared with the growth of pure BNBP and BCNBP. SPEM results clearly demonstrate that 4,4′-dibromobiphenyl (DBBP) can invert the polarity for both crystals. Phenomena reported in this paper belong to the most striking processes seen for molecular crystals, demonstrated by a stochastic process giving rise to symmetry breaking. We encounter here further examples supporting the general thesis that monodomain polar molecular crystals for fundamental reasons cannot exist. |
| Databáze: | OpenAIRE |
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