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Open AccessArticle

The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile

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
Advanced Light Source, 1 Cyclotron Road, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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
Department of Earth & Planetary Sciences, University of California, Santa Cruz, 1156 High Street Santa Cruz, CA 95064, USA
Present address: Diamond Light Source, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Harwell Oxford, Didcot OX11 0QX, UK
Present address: Physical and Life Sciences, Physics Division, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
Dpto. DCITIMAC, Facultad de Ciencias, Universidad de Cantabria, 39005 Santander, Spain
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;
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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    Description: CCDC 1911442-1911459 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via (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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