The title compounds, C18H15N3O4 and C17H14ClN3O3, are heterocyclic 1,3,4-oxa-diazole derivatives which differ from each other in the groups attached to the carbon atoms: a meth-oxy-phenyl ring and a benzo-nitrile group in (I) and a chloro-phenyl ring and an acetamide group in (II). Short intra-molecular C-H⋯O hydrogen bonds occur in both mol-ecules. The crystal structure of (I) features C-H⋯N hydrogen bonds, while in the crystal structure of (II), N-H⋯N, C-H⋯N and C-H⋯O hydrogen bonds are observed.
Keywords: crystal structure; intermolecular C—H⋯N and N—H⋯N hydrogen bonds; intramolecular C—H⋯O interactions; oxadiazole derivatives; superposition.