Ditopic halogen bonding with bipyrimidines and activated pyrimidines.

The potential of pyrimidines to serve as ditopic halogen-bond acceptors is explored. The halogen-bonded cocrystals formed from solutions of either 5,5'-bipyrimidine (C8H6N4) or 1,2-bis(pyrimidin-5-yl)ethyne (C10H6N4) and 2 molar equivalents of 1,3-diiodotetrafluorobenzene (C6F4I2) have a 1:1 composition. Each pyrimidine moiety acts as a single halogen-bond acceptor and the bipyrimidines act as ditopic halogen-bond acceptors. In contrast, the activated pyrimidines 2- and 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine (C14H13N3) are ditopic halogen-bond acceptors, and 1:1 halogen-bonded cocrystals are formed from 1:1 mixtures of each of the activated pyrimidines and either 1,2- or 1,3-diiodotetrafluorobenzene. A 1:1 cocrystal was also formed between 2-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4-diiodotetrafluorobenzene, while a 2:1 cocrystal was formed between 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4-diiodotetrafluorobenzene.