Synthesis and solid state self-assembly of a 1,4-diazepine derivative: Water cluster as molecular glue and conformational isomerism

Diazepine (a seven membered heterocycle) derivatives have emerged as privileged structures in chemical biology and medicinal chemistry. In this article, synthesis of a 1, 4-diazepine derivative 4 from flavone 3 in excellent yield is described. The solid state self-assembly pertaining to diazepine derivative 4 was investigated with X-ray crystallography. Fascinatingly, the solid state structure of 4 represents a remarkable example of water cluster acting as structural glue to instigate conformational isomerism and hence facilitate the crystallization process by compensating the imbalance of hydrogen-bond donors and acceptors. NBO and QTAIM based calculations show that the hydrogen-bonding network of water molecules and hyper conjugative interactions play a vital role for stabilization of structure in the solid state. To our knowledge, presented here is the first illustration of any solvent cluster stabilizing the solid-state structure in a diazepine family. In addition, the crystal structure of flavone 3 hitherto not reported is also reported. (C) 2020 Elsevier B.V. All rights reserved.