Lack of Cooperativity in the Triangular X3 Halogen-Bonded Synthon?

Justyna Dominikowska; Agnieszka J Rybarczyk-Pirek; Célia Fonseca Guerra

doi:10.1021/acs.cgd.0c01410

Lack of Cooperativity in the Triangular X₃ Halogen-Bonded Synthon?

Cryst Growth Des. 2021 Jan 6;21(1):597-607. doi: 10.1021/acs.cgd.0c01410. Epub 2020 Dec 16.

Authors

Justyna Dominikowska^{1

2}, Agnieszka J Rybarczyk-Pirek¹, Célia Fonseca Guerra^{2

3}

Affiliations

¹ Theoretical and Structural Chemistry Group, Department of Physical Chemistry, Faculty of Chemistry, University of Lodz, Pomorska 163/165, 90-236 Łódź, Poland.
² Department of Theoretical Chemistry and Amsterdam Centre for Multiscale Modelling, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
³ Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.

Abstract

We have investigated 44 crystal structures, found in the Cambridge Structural Database, containing the X₃ synthon (where X = Cl, Br, I) in order to verify whether three type II halogen-halogen contacts forming the synthon exhibit cooperativity. A hypothesis that this triangular halogen-bonded motif is stabilized by cooperative effects is postulated on the basis of structural data. However, theoretical investigations of simplified model systems in which the X₃ motif is present demonstrate that weak synergy occurs only in the case of the I₃ motif. In the present paper we computationally investigate crystal structures in which the X₃ synthon is present, including halomesitylene structures, that are usually described as being additionally stabilized by a synergic interaction. Our computations find no cooperativity for halomesitylene trimers containing the X₃ motif. Only in the case of two other structures containing the I₃ synthon a very weak or weak synergy, i.e. the cooperative effect being stronger than -0.40 kcal mol^-1, is found. The crystal structure of iodoform has the most pronounced cooperativity of all investigated systems, amounting to about 10% of the total interaction energy.