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Open AccessArticle

The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile

1
Centre for Science at Extreme Conditions and EaStCHEM School of Chemistry, The University of Edinburgh, King’s Buildings, West Mains Road, Edinburgh, Scotland EH9 3FD, UK
2
Advanced Light Source, 1 Cyclotron Road, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
3
Centre for Science at Extreme Conditions and School of Engineering, The University of Edinburgh, King’s Buildings, West Mains Road, Edinburgh, Scotland EH9 3FD, UK
4
Department of Earth & Planetary Sciences, University of California, Santa Cruz, 1156 High Street Santa Cruz, CA 95064, USA
5
Present address: Diamond Light Source, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Harwell Oxford, Didcot OX11 0QX, UK
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Present address: Physical and Life Sciences, Physics Division, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
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Dpto. DCITIMAC, Facultad de Ciencias, Universidad de Cantabria, 39005 Santander, Spain
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Dpto. Física Aplicada, Facultad de Ciencias, Universidad de Cantabria-IDIVAL, 39005 Santander, Spain
*
Authors to whom correspondence should be addressed.
Molecules 2019, 24(10), 2018; https://doi.org/10.3390/molecules24102018
Received: 29 April 2019 / Revised: 20 May 2019 / Accepted: 22 May 2019 / Published: 27 May 2019
The crystal structure of 4-iodobenzonitrile, which is monoclinic (space group I2/a) under ambient conditions, contains chains of molecules linked through C≡N···I halogen-bonds. The chains interact through CH···I, CH···N and π-stacking contacts. The crystal structure remains in the same phase up to 5.0 GPa, the b axis compressing by 3.3%, and the a and c axes by 12.3 and 10.9 %. Since the chains are exactly aligned with the crystallographic b axis these data characterise the compressibility of the I···N interaction relative to the inter-chain interactions, and indicate that the halogen bond is the most robust intermolecular interaction in the structure, shortening from 3.168(4) at ambient pressure to 2.840(1) Å at 5.0 GPa. The π∙∙∙π contacts are most sensitive to pressure, and in one case the perpendicular stacking distance shortens from 3.6420(8) to 3.139(4) Å. Packing energy calculations (PIXEL) indicate that the π∙∙∙π interactions have been distorted into a destabilising region of their potentials at 5.0 GPa. The structure undergoes a transition to a triclinic ( P 1 ¯ ) phase at 5.5 GPa. Over the course of the transition, the initially colourless and transparent crystal darkens on account of formation of microscopic cracks. The resistance drops by 10% and the optical transmittance drops by almost two orders of magnitude. The I···N bond increases in length to 2.928(10) Å and become less linear [<C−I∙∙∙N = 166.2(5)°]; the energy stabilises by 2.5 kJ mol−1 and the mixed C-I/I..N stretching frequency observed by Raman spectroscopy increases from 249 to 252 cm−1. The driving force of the transition is shown to be relief of strain built-up in the π∙∙∙π interactions rather than minimisation of the molar volume. The triclinic phase persists up to 8.1 GPa. View Full-Text
Keywords: high pressure; halogen bonding; intermolecular interactions high pressure; halogen bonding; intermolecular interactions
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    Link: http://www.ccdc.cam.ac.uk/conts/retrieving.html
    Description: CCDC 1911442-1911459 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44 1223 336033; E-mail: [email protected]
MDPI and ACS Style

Giordano, N.; Afanasjevs, S.; Beavers, C.M.; Hobday, C.L.; Kamenev, K.V.; O’Bannon, E.F.; Ruiz-Fuertes, J.; Teat, S.J.; Valiente, R.; Parsons, S. The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile. Molecules 2019, 24, 2018.

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