Different packing motifs mediated by weak inter-actions and polymorphism in the crystal structures of five...

The syntheses and crystal structures of five 2-benzyl-idene-1-benzosuberone [1-benzosuberone is 6,7,8,9-tetra-hydro-5H-benzo[7]annulen-5-one] derivatives, viz. 2-(4-meth-oxy-benzyl-idene)-1-benzosuberone, C₁₉H₁₈O₂, (I), 2-(4-eth-oxy-benzyl-idene)-1-benzosuberone, C₂₀H₂₀O₂, (II), 2-(4-benzyl-benzyl-idene)-1-benzosuberone, C₂₅H₂₂O₂, (III), 2-(4-chloro-benzyl-idene)-1-benzosuberone, C₁₈H₁₅ClO, (IV) and 2-(4-cyano-benzyl-idene)-1-benzosuberone, C₁₉H₁₅NO, (V), are described. The conformations of the benzosuberone fused six- plus seven-membered ring fragments are very similar in each case, but the dihedral angles between the fused benzene ring and the pendant benzene ring differ somewhat, with values of 23.79 (3) for (I), 24.60 (4) for (II), 33.72 (4) for (III), 29.93 (8) for (IV) and 21.81 (7)° for (V). Key features of the packing include pairwise C-H⋯O hydrogen bonds for (II) and (IV), and pairwise C-H⋯N hydrogen bonds for (V), which generate inversion dimers in each case. The packing for (I) and (III) feature C-H⋯O hydrogen bonds, which lead to [010] and [100] chains, respectively. Weak C-H⋯π inter-actions consolidate the structures and weak aromatic π-π stacking is seen in (II) [centroid-centroid separation = 3.8414 (7) Å] and (III) [3.9475 (7) Å]. A polymorph of (I) crystallized from a different solvent has been reported previously [Dimmock et al. (1999 ▸) J. Med. Chem. 42, 1358-1366] in the same space group but with a packing motif based on inversion dimers resembling that seen in (IV) in the present study. The Hirshfeld surfaces and fingerprint plots for (I) and its polymorph are com-pared and structural features of the 2-benzyl-idene-1-benzosuberone family of phases are surveyed.