Abstract
Sulfur is a widely used halogen bond (XB) acceptor, but only a limited number of neutral XB acceptors with bifurcated sp3-S sites have been reported. In this work a new bidentate XB acceptor, 1-(4-pyridyl)-4-thiopyridine (PTP), which combines sp3-S and sp2-N acceptor sites, is introduced. Three halogen bonded cocrystals were obtained by using 1,4-diiodobenzene (DIB), 1,4-diiodotetrafluorobenzene (DIFB), and iodopentafluorobenzene (IPFB) as XB donors and PTP as acceptor. The structures of the cocrystals showed some XB selectivity between the S and N donors in PTP. However, the limited contribution of XB to the overall molecular packing in these three cocrystals and the results from DSC measurements clearly point out the synergetic influence and interplay of all noncovalent interactions in crystal packing of these compounds.
Highlights
Halogen bond (XB) is a noncovalent interaction occurring between an electrophilic region (σ-hole) of a halogen atom (XB donor) in a molecular moiety and a nucleophilic atom (XB acceptor) in the same or another moiety [1]
Unlike the sp2 nitrogen atoms (sp2 -N), both sp2 sulfur atoms (sp2 -S) and sp3 sulfur atoms (sp3 -S) can act as bifurcated XB acceptors in three-centered halogen bonds, due to the two available lone pairs on sulfur [9]
The results suggest that other type of intermolecular interactions than XBs could be the dominating factors behind the thermal stability in cocrystals 1–3
Summary
Halogen bond (XB) is a noncovalent interaction occurring between an electrophilic region (σ-hole) of a halogen atom (XB donor) in a molecular moiety and a nucleophilic atom (XB acceptor) in the same or another moiety [1]. Just like the hydrogen bond, XB is highly directional [6,7,8]. Unlike the sp2 -N, both sp2 -S and sp3 -S can act as bifurcated XB acceptors in three-centered halogen bonds, due to the two available lone pairs on sulfur [9]. Both sp2 -O and sp3 -O can function as multidentate XB acceptors. A CCDC survey (C-X· · · S, C-X· · · O, X=Br, I; no organometallic complexes; CSD version 5.41, November 2019) gave 539 structures with
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