Molecular and Crystal Structures of Novel Second-Order Nonlinear Optical Crystals: α,α′-Dibenzylidenecycloalkanones

Abstract X-Ray crystallographic analyses have been performed for the crystals of α,α′-dibenzylidenecycloalkanone (DBCA) derivatives which preferentially crystallize in non-centrosymmetric space groups and become second-order nonlinear optical crystals. We examined the obtained structures while paying attention to the intermolecular short contacts common to their structure. As a result, relatively short C–H···O contacts between the cycloalkanone rings were found for 8 out of 10 DBCA derivatives. The C–H···O distances for all cyclopentanone derivatives are almost the same as the sum of the van der Waals radius of carbon and that of oxygen; also, the geometrical characteristics found from the C–H···O contacts are consistent with the C–H···O hydrogen bond. The derivatives form a non-centrosymmetric one-dimensional chain with this contact. Their non-centrosymmetric crystal structures are led not only by their molecular shape, but also by this C–H···O interaction.