Role of chloroform and dichloromethane solvent molecules in crystal packing: an interaction propensity study.

Using the Cambridge Structural Database (CSD), it is shown that the acidic C-H donors of chloroform and dichloromethane, respectively, form hydrogen bonds with N, O, S, halides or carbon-bound halogens in 82% and 77% of structures in which such interactions can occur. This hydrogen-bond potency is retained to a significant degree even in the presence of the more conventional O-H and N-H donors. The hydrogen-bond propensities exhibited by the C-H protons in CHCl3 and CH2Cl2 are similar to those of the acetylenic C-C≡C-H proton. However, involvement of the Cl atoms of CHCl3 and CH2Cl2 in non-bonded interactions is rather limited: the propensities for formation of (O or N)-H...Cl bonds are only 6% in both cases, while the propensities for the formation of halogen-halogen bonds is generally < 15%, with only Cl...Br interactions having slightly higher values. While C(phenyl)-H...Cl interactions are commonly observed, they are of low propensity and have distances at the upper end of the van der Waals limit. We conclude that the acidic C-H protons in chloroform and dichloromethane solvent molecules play a clear role in the involvement of these molecules in molecular aggregation in crystal structures, and this is exemplified by hydrogen-bond predictions made using the statistical propensity tool which is now part of the CSD system.