Edge-to-edge aryl C-H center dot center dot center dot N dimer: a new supramolecular synthon

Study of the lattice packing in the crystal structures of the diquinoline compounds 1 [C23H18N2, P (1) over bar, a = 6.1953(8), b = 11.427(2), c = 12.686(2) Angstrom, a = 108.428(7), beta = 92.189(8), gamma = 103.437(7)degrees, Z = 2, R = 0.038] and 2 . CHCl3 [C23H16Br2N2 . CHCl3, P2(1)/c, a = 9.865(3), b = 15.307(3), c = 17.946(5) Angstrom, beta = 122.12(1)degrees, Z = 4, R = 0.031] reveals a previously unrecognised mode of intermolecular attraction which we term-the edge-to-edge aryl C-H ... N dimer. Examination of the Cambridge Structural Database shows that this type of contact is present in a wide range of nitrogen-containing aromatic solids. In all 54 identified cases the two weak intermolecular hydrogen bonds are identical producing asymmetrical dimer and, in all cases but one, the arrangement created is centrosymmetric. Hence this new packing mode represents a predictable new synthon for supramolecular assembly.