SHAPE MIMICRY AS A DESIGN TOOL IN CRYSTAL ENGINEERING

The pseudosymmetric chiral sulphoxide 1 was designed with two segments of nearly identical shape but with significantly different electron-d onor/acceptor properties. Based on the known high statistical preferen ce for organics to pack in one of the centrosymmetric space groups, fo rmation of molecular crystals of enantiomerically pure 1 was predicted to occur with pseudocentrosymmetry, with 1 also playing the role of i ts enantiomer and packing as would the racemate. Such a packing motif would lack true centrosymmetry, resulting in a polar axis for the crys tal and net additivity of the vectors from nitrogen to sulphur (the di rection of polarizability for the molecules). Enantiomeric sulphoxide 1 does form molecular crystals with false centrosymmetry, mimicking P2 (1)/c, and with a substantial net directionality of polarizability vec tors. In contrast, enantiomeric sulphoxides 3 and 4 form molecular cry stals where the vectors from nitrogen to sulphur in neighbouring molec ules are essentially opposed.