Hydrogen-bonded chains formed by 5,5-diethylbarbituric acid and bipyridyl tectons

Supramolecular interactions play an important role in determining the solid-state structures of many molecular species. In this study, we describe the role of pyridyl-based molecules in forming hydrogen-bonded chains with 5,5-diethylbarbituric acid (DEB). The single crystal X-ray structures of three hydrogen-bonded co-crystals all exhibit one-dimensional chains formed via N–H…N interactions between pyridyl hydrogen bond acceptors and N–H hydrogen bond donors of DEB. Subtle differences are observed between the three related co-crystals. Although both DEB·4,4’-bipy, 1, and DEB·diaz, 2, (diaz = 2,7-diazapyrene) adopt similar one-dimensional chains with a 1:1 DEB:bipyridyl stoichiometry, π–π interactions play a significant role in the solid-state arrangement of 2 only. In 2(DEB)·dpb, 3, (dpb = 1,4-bis(4-pyridyl)-benzene), an alternative 2:1 DEB:bipyridyl stoichiometry is observed. Dimeric DEB hydrogen-bonded units are linked into hydrogen-bonded chains through further hydrogen bonding. The co-crystal DEB·pypm, 4, (pypm = 5-(4-pyridyl)pyrimidine), also forms dimeric DEB hydrogen-bonded units which interact with the pyridyl groups of pypm. However, the pyrimidine groups of pypm do not participate in hydrogen bonding to DEB molecules and as a result discrete dimeric 2(DEB)·2(pypm) units are formed.