Conformational polymorphism and aromaticity in crystalline dibenzotetraaza[14]annulene derivatives

The structures of two single crystal modifications, orange and yellow, of 7,16-dibenzoyl-6,8,15,17-tetramethyl-5,14-dihydrodibenzo [b,i][1,4,8,11]tetraazacyclotetradecine were determined in room and low temperatures. The aromaticity of the 14-membered macrocyclic ring system was studied with the use of HOMA index and compared to the values calculated for the structures found in the Cambridge Structural Database System. The nature of the polymorphism of the investigated molecules was elucidated. The molecules of the orange and yellow modifications differ in the mutual orientation of the benzoyl groups. The molecular conformation in the yellow crystals is stabilized by two intramolecular hydrogen bonds, C–H· · ·OyC, which do not occur in the orange modification. Weak, but numerous, intermolecular bonds of this type occur in both modifications, but in the orange polymorph a p–p interaction is also observed, while in the yellow modification a C–H· · ·N intermolecular bond is formed. q 2003 Elsevier B.V. All rights reserved.