Novel 1,3-diethyl-2-thiobarbiturates of 2,2'-bipyridine and 1,10-phenanthroline: Synthesis, crystal structure and thermal stability

Co-crystallization of 1,3-diethyl-2-thiobarbituric acid (HDetba) with 2,2′-bipyridine (Bipy) and 1,10-phenanthroline (Phen) results in preparing a salt co-crystal, BipyH(Detba)(HDetba) (1), and the salt, PhenH(Detba)·H₂O (2). The compounds are characterized by single–crystal and powder X–ray diffraction and TG-DSC. The nitrogen atoms of BipyH⁺ adopt a cis conformation and the NCCN torsion angle is −17.3(1)º. There are six intermolecular hydrogen bonds OH⋯O, NH⋯O, CH⋯O and CH⋯S in (1) which form a 2D plane network. One Detba^– ion and one HDetba molecule form a pair by means of OH⋯O hydrogen bonds. Detba⁻ anions in (2) do not form dimers, they are connected by NH⋯O, CH⋯S, and CH⋯O hydrogen bonds only with PhenH⁺ cations and water molecules which form a 3D net. Different π−π interactions between the rings are found in (1)−(2).