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The title compound, 2,2':4,4'':4',4'''-quaterpyridine (Qtpy), C 20 H 14 N 4 , crystallizes in the triclinic P space group and has half of the mol-ecule in the asymmetric unit, corresponding to 4,4'-bi-pyridine (4,4'-bpy) that serves as the building block for the mol-ecule. C 4,4'-bpy -N-C 4,4'-bpy and/or N-C 4,4'-bpy -C 4,4'-bpy bond-angle parameters show that the 4,4'-bpy ligands are highly rigid, displaying values lower than the linear bond angle of 180°. In the crystal, the 4,4'-bpy units are seen to be facing each other in relatively close proximity. The most important inter-actions on the Hirshfeld Surface of the compound are C-H⋯N/H⋯N-C inter-actions (constituting 10.6% and 7.6% of the total surface)., (© Aderinto et al. 2023.)

The title compound, C 7 H 4 F 3 NO 2 , 3-tri-fluoro-methyl-1 H -pyrrolo-[1,2- c ]oxazol-1-one, is the first crystal structure of the pyrrolo-[1,2- c ]oxazole ring system: the fused ring system is almost planar (r.m.s. deviation = 0.006 Å). In the crystal, weak C-H⋯O and C-H⋯F hydrogen bonds link the mol-ecules into [001] chains and π-π stacking inter-actions consolidate the structure.