A variable-temperature X-ray diffraction and theoretical study of conformational polymorphism in a complex organic molecule (DTC).

Two conformational crystal polymorphs of 3-diethylamino-4-(4-methoxyphenyl)-1,1-dioxo-4-1λ,2-thiazete-4-carbonitrile (DTC) have been analyzed in the 100 K-room temperature range by single crystal X-ray diffraction and high quality DFT calculations. DTC has strongly polar as well as aliphatic substituents but no hydrogen bonding groups, and thus qualifies as a test molecule for the relative importance of electrostatic dispersion-repulsion terms. The two polymorphs have the same 2/ space group and differ by a flipping of the -OCH group, the two conformations being almost equi-energetic and separated by a low barrier.