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Peculiar orientational disorder in 4-bromo-4′-nitrobiphenyl (BNBP) and 4-bromo-4′-cyanobiphenyl (BCNBP) leading to bipolar crystals
- Source :
- IUCrJ, Vol 3, Iss 3, Pp 219-225 (2016)
- Publication Year :
- 2016
- Publisher :
- International Union of Crystallography, 2016.
-
Abstract
- 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.
- Subjects :
- orientational disorder
bipolar crystals
structural defects
Crystallography
QD901-999
Subjects
Details
- Language :
- English
- ISSN :
- 20522525
- Volume :
- 3
- Issue :
- 3
- Database :
- Directory of Open Access Journals
- Journal :
- IUCrJ
- Publication Type :
- Academic Journal
- Accession number :
- edsdoj.fa92f7f5d82d4d9ebad4466fdc571692
- Document Type :
- article
- Full Text :
- https://doi.org/10.1107/S2052252516006709