Sarah N. Johnson,*,1 Thomas L. Ellington,1 Jorge Nevarez,1 Nicholas Sparks,1 Duong Ngo,1 Arnold L. Rheingold,2 Davita L. Watkins,1 and Gregory S. Tschumper1
1. Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677
2. Department of Chemistry, University of California: San Diego, La Jolla, CA 92093
Email: snjohns4@go.olemiss.edu
The present study focuses on if furan and thiophene substituents have an effect on the solid-state properties of and the non-covalent interactions in co-crystals formed between pentafluoro (iodoethynyl) benzene (F5BAI; XB donor) and a pyridine disubstituted with either a furan or thiophene (PyrFur2 or PyrThio2; XB acceptors). Spectroscopic and thermal analyses of 1:1 mixtures provide indirect evidence of halogen bond (XB) formation whereas X-ray crystallography provides direct evidence that XB and π-stacking are the most prevalent contacts in both co-crystals. Density functional theory computations provide insight into the relative energetics of the various contacts observed in the co-crystals [1-3]. The global hybrid M06-2X density functional is employed in conjunction with a triple-ζ correlation consistent basis set augmented with diffuse functions on all atoms and a relativistic pseudopotential on iodine centers (aug-cc-pVTZ-PP) in order to compute the electronic interaction energies (with and without the Boy-Bernardi counterpoise procedure) of all pairwise contacts that have intermolecular separations of ≤ 5 Å. Within both co-crystals approximately twenty unique contacts are identified that satisfy this distance threshold, where XB and π-stacking interactions are significantly stronger (between −12.0 and −6.8 kcal mol−1) than all other attractive interactions (≤ −2.1 kcal mol−1).
References:
[1] Nguyen S. T. et al. (2018) Cryst. Growth Des., 18, 3244-3254.
[2] Nguyen S. T. et al. (2016) Cryst. Growth Des., 16, 6648-6653.
[3] Wilson J. et al. (2015) RSC Adv., 5, 82544-82548.