Polymorphism of 7-dimethylaminocyclopenta[c]coumarin: packing analysis and generation of trial crystal structures

The crystal structures of two polymorphs of the title compound [ Pbca and Pna 2 1 ; Jasinski & Woudenberg (1995). Acta Cryst. C 51 , 107–109] were analysed. Packing energies and indices were compared. Molecules in the two forms show a slight conformational difference; both conformers were packed in some of the most frequent space groups for organic molecules ( P 2 1 , P 2 1 / c , P 2 1 2 1 2 1 and Pna 2 1 ) using a computer program for crystal structure generation and prediction ( PROMET 3). The results of such calculations are used to provide tentative explanations for the preference of the two conformers for centrosymmetric and non-centrosymmetric space groups. Several comments on general problems encountered in crystal structure prediction are also presented, concerning in particular the multi-minima structure of the potential energy hypersurface.