Halogen-Bond Preferences in Co-crystal Synthesis

Abstract

To examine the possibility of establishing a hierarchy of the relative importance of different halogen bonds in the solid state, twelve co-crystallization experiments were performed between three different ditopic halogen-bond acceptors, 1,1 0 -bis(pyridin-4-ylmethyl)-2,2 0 -biimidazole (A1), 1,1 0 -bis(pyridin-3-ylmethyl)-2,2 0 -biimidazole (A2) and 1,1 0 -bis(pyridin-2-ylmethyl)-2,2 0 -biimidazole (A3) and four perfluoroiodoalkanes. A ranking of potentially competing acceptor-sites was based on calculated molecular electrostatic surface potentials using DFT; the pyridine nitrogen atom found to be the best acceptor in all three acceptor molecules. An analysis of the outcome of all twelve attempted reactions using IR spectroscopy showed that eight of the twelve attempts resulted in a cocrystal, the equivalent of a 67 % total supramolecular yield. Six crystal structures were obtained and all show that halogen bonding involves the best acceptor site (pyridine) as ranked by the electrostatic potentials. The supramolecular yield increased with increasing charge on the acceptor site thereby underlying the importance of electrostatics in practical supramolecular synthesis of co-crystals driven by halogen bonding. Graphical Abstract A ranking of potentially competing halogen bond acceptor-sites was achieved using calculated molecular electrostatic surface potentials and successfully implemented in the practical synthesis of co-crystals with the desired connectivity.

Experimental and Theoretical Investigation of Structures, Stoichiometric Diversity, and Bench Stability of Cocrystals with a Volatile Halogen Bond Donor

“…Our interest in halogen-bonding properties of phen and acr is based on their polyaromatic heterocyclic structure 29 which provides a simple entry into halogen bond acceptors that are sterically and electronically different from the much more investigated pyridine-or azole-based acceptors. [30][31][32][33][34][35][36][37][38] Furthermore, the similarity of molecular structures of acr and phen offers an excellent opportunity to investigate the effect of exchanging aromatic C-H and N functionalities on molecular self-assembly in the solid state, and in particular on the formation of isostructural solids. 26,27,39,40 Both acr and phen are weak bases, with respective pKa values of 5.58 and 1.23, 28,41,42 and have been used extensively as components of hydrogen-bonded salts and cocrystals.…”

A new tecton with parallel halogen-bond donors: a path to supramolecular rectangles

“…The halogen bond (Meazza et al, 2013;Prä sang et al, 2009;Desiraju et al, 2013;Aakerö y, Wijethunga, Desper & Moore, 2015) has become one of the most important new tools in supramolecular chemistry (Desiraju, 2001;Lehn, 1980Lehn, , 1995, partly because it has several features that are parallel to those of the hydrogen bond (Meazza et al, 2013;Priimagi et al, 2013;Tothadi & Desiraju, 2013;Metrangolo et al, 2005). In some situations, however, the halogen bond may be a superior synthetic tool because of a more pronounced directionality (Gavezzotti, 2008;Crihfield et al, 2003;Karpfen, 2003;Shen & Jin, 2011), a lack of inherent self-complementarity (which can limit heteromeric synthesis), and reduced chemical sensitivity to pH changes.…”

Construction of Coordination Polymers from Semirigid Ditopic 2,2′-Biimidazole Derivatives: Synthesis, Crystal Structures, and Characterization

“…These ligands display pyridine (N Py ) and imidazole (N Im ) coordination groups which differ in their coordination ability (N Py coordination ability is higher than the N Im ). [28][29][30] According to the structures of these eight CPs, we have found that the final structure can be influenced by the structure of the ligand, Both the structures and the properties can be adjusted by choice of the metal and by modifying the reaction conditions.…”