C–halogen…O supramolecular synthons: in situ cryocrystallisation of 1,2-dihalotetrafluoroethane/HMPA adducts

Abstract

The in situ cryocrystallisation technique has been used to obtain four adducts between hexamethylphosphortriamide and 1,2-dihalotetrafluoroethanes having iodine, bromine and chlorine as halogen-bonding donor atoms. These systems allowed for a precise comparison of different CZX· · ·O synthons. The effectiveness and reliability of the pharmacologically important CZCl· · ·O synthons are proven.

The Halogen Bond

“…For instance, in halogen-bonded adducts where pyridines are the XB acceptors, the C–X group is almost coplanar with the pyridyl ring, and the two C–N···X angles are close to 120°. , The same geometrical features are observed for other nitrogen heteroaromatics such as pyrazine or quinoline. − When carbonyl groups act as XB acceptors, the oxygen may function as both a monodentate and a bidentate site, and the XB donor(s) are pinned in a trigonal planar geometry. Sulfonyl , and phosphoryl groups behave similarly to carbonyl moieties, and also imines form XBs along the respective n-pair axis. XBs around ethers, , thioethers, , and amines , usually adopt a tetrahedral arrangement with preferential axial directions for the XBs around hexacyclic amines and equatorial directions for hexacyclic thioethers (Figure ).…”

“…Examples reported in the CSD usually involve oxygen 727 and sulfur 78 atoms, which frequently behave as bifurcated sites ( Figure 76 , FEQVON and NUSBUZ). This ability of oxygen atoms, discovered thanks to in situ cryocrystallization, allowed for the obtainment of 1D polymeric architectures between 1,3-dibromotetrafluorobenzene, 178 or 1,2-dihalotetrafluoroethane, 179 and dimethyl sulfoxide (DMSO) or hexamethylphosphoramide (HMPA).…”

“… 172 − 174 When carbonyl groups act as XB acceptors, the oxygen may function as both a monodentate 175 and a bidentate 176 site, and the XB donor(s) are pinned in a trigonal planar geometry. Sulfonyl 177 , 178 and phosphoryl 179 groups behave similarly to carbonyl moieties, and also imines 180 form XBs along the respective n-pair axis. XBs around ethers, 56 , 181 thioethers, 182 , 183 and amines 184 , 185 usually adopt a tetrahedral arrangement with preferential axial directions for the XBs around hexacyclic amines 186 and equatorial directions for hexacyclic thioethers 64 ( Figure 14 ).…”

Halogen Bonding in Supramolecular Chemistry

“…More recently, Metrangolo, Resnati, and co-workers cocrystallized 1,2-dihalotetrafluoroethanes with HMPA using in situ cryocrystallization techniques to investigate the C–X···O (X = Cl, Br, I) synthons further. In the isostructural series of cocrystals, both the XB donor and acceptor tectons behave as bidentate modules with HMPA accepting two XBs.…”

“…The review encompassed both organic and inorganic oxoanions with a variety of XB donor molecules and the use of XB with anions to facilitate solid-state self-assembly. More recently, the same authors discussed the use of anions as XB acceptors: due to the more diffuse, and less directional, electron cloud surrounding the anionic species, the prediction and control of the stoichiometry and geometry of any architectures that may be formed is much more difficult, when compared with a lone pair on a heteroatom . However, this allows anions to behave as mono-, bi-, and polydentate XB acceptors.…”