Polymorphism in some new bis-hydrazone compounds.

We describe the polymorphism of four new bis-hydrazone compounds, namely butane-2,3-dione 2,3-bis{[bis(4-fluorophenyl)methylidene]hydrazone}, CHFN (1), butane-2,3-dione 2,3-bis{[bis(4-chlorophenyl)methylidene]hydrazone}, CHClN (2), butane-2,3-dione 2,3-bis{[bis(4-methylphenyl)methylidene]hydrazone}, CHN (3), and butane-2,3-dione 2,3-bis({bis[4-(dimethylamino)phenyl]methylidene}hydrazone), CHN (4), derived by the condensation reaction between substituted benzophenone hydrazone and butane-2,3-dione. Concomitant polymorphism has been observed in 1, 2 and 3. Overlays of molecules of the different polymorphs indicate that there is conformational adjustment in the crystal structures of the polymorphs of 1 and 2, i.e. packing polymorphism, which was confirmed by a computational study. On the other hand, conformational change was observed in the cases of the polymorphs of compounds 3 and 4, i.e. conformational polymorphism.