Orientational disorder: A key to understand polarity of molecular crystals
| Autor: | Matthias Burgener, Galina Dulcevscaia, Jürg Hulliger, Khadidja Brahimi |
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| Rok vydání: | 2014 |
| Předmět: |
Polarity reversal
Chemistry Polarity (physics) Organic Chemistry Monte Carlo method 02 engineering and technology 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Acceptor Symmetry (physics) 0104 chemical sciences Analytical Chemistry Pyroelectricity Inorganic Chemistry Crystallography Chemical physics Molecule 0210 nano-technology Spectroscopy Solid solution |
| Zdroj: | JOURNAL OF MOLECULAR STRUCTURE |
| DOI: | 10.1016/j.molstruc.2014.02.042 |
| Popis: | Polarity of molecular crystals is understood here as a result of 180° orientational disorder of asymmetrical building blocks. Symmetry arguments based on (i) a single rotational degree of freedom, (ii) the finite size of crystals and (iii) interactions in between asymmetrical molecules lead to the conclusion that such crystals should express a bi-polar (∞/∞m) average state of zero polarity. This basic property of molecular crystals is exemplified by forming solid solutions of 4-iodo-4′-nitro-biphenyl (INBP) and symmetrical bi-phenyls (BP: A-π-A, D-π-D; A: acceptor; D: donor). Monte Carlo simulations based on a layer-by-layer growth model predict a reversal of the bi-polar state of pure INBP by forming a solid solution of (INBP) 1 − x (D-π-D) x . In the case of the addition of A-π-A reversal as found for pure INBP is promoted, i.e. needs less growth steps (layers) to be accomplished. Real crystals representing solid solutions were grown from 2-butanon solutions using symmetrical BPs. Scanning pyroelectric microscopy confirmed the qualitative behavior seen in Monte Carlo simulations. These findings represent an experimentum crucis supporting the general validity of the theory of stochastic polarity formation applied to single component or solid solution molecular crystals. |
| Databáze: | OpenAIRE |
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