The crystal structure of 4 '-{4-[(2,2,5,5-tetramethyl-N-oxyl-3-pyrrolin-3-yl)ethynyl]phenyl}-2,2 ':6 ',2 ''-terpyridine

The terpyridine group of the title compound, C31H27N4O, assumes an all-transoid conformation and is essentially planar with the dihedral angles between the mean planes of the central pyridine and the two outer rings amounting to 3.87 (5) and 1.98 (5)degrees. The pyrroline-N-oxyl group commonly seen in such nitroxyls is found in the title structure and the mean plane of the pyrroline ring subtends a dihedral angle of 88.44 (7)degrees to the mean plane of the central pyridine ring. The intramolecular separation between the nitrogen atom of the central pyridine unit of the terpyridine group and the nitroxyl group is 14.120 (2) angstrom. In the crystal, the molecules are arranged in layers stacked along [001]. Slipped face-to-face pi-pi interactions between the pyridine rings are observed along this direction with the shortest centroid-centroid distances amounting to 3.700 (1) and 3.781 (1) angstrom. Furthermore, edge-on C-H center dot center dot center dot pi interactions between the phenylene rings of neighbouring molecules are observed along this direction. A two-dimensional C-H center dot center dot center dot O hydrogen-bonded network is formed within the (010) plane. The shortest O center dot center dot center dot O separation between neighbouring molecules is 5.412 (3) angstrom.