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 Pna2(1); Jasinski & Woudenberg (1995). Acta Cryst. C51, 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 (P2(1), P2(1)/c, P2(1)2(1)2(1) and Pna2(1)) using a computer program for crystal structure generation and prediction (PROMET3). 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.