|Schmidt, M.; Wittmann, J.J.; Kress, R.; Schneider, D.; Steuernagel, S.; Schmidt, H.-W.; Senker, J.: Crystal Structure of a Highly Efficient Clarifying Agent for Isotactic Polypropylene, Crystal Growth & Design, 12(5), 2543-2551 (2012) -- DOI: 10.1021/cg300151s|
Using a combined approach based on X-ray powder diffraction and solid-state NMR spectroscopy we were able to determine the crystal structure of 1,3,5-tris(2,2-dimethylpropionylamino)benzene, an efficient clarifying agent for isotactic polypropylene. The XPRD data and 1D solid-state NMR experiments allowed excluding most of the possible primitive orthorhombic space groups with the exception of 11. The structure solution was carried out using real space methods including a close-contact penalty. Four space groups lead to reasonable wRp values below 10 %. 13C13C double quantum (DQ) experiments of the labeled carbonyl group were measured with a supercycled symmetry based dipolar recoupling sequence. Taking into account the wRp values after Rietveld refinement as well as simulations of DQ build-up curves based on nine spin systems, the space group P212121 is clearly favored. The largest dipolar coupling within these spin systems was about 60 Hz corresponding to a distance of 5 Å. 1,3,5-tris(2,2-dimethylpropionylamino)benzene crystallizes in an orthorhombic metric (a = 14.91(5) Å, b = 24.05(8) Å, c = 6.80(2) Å). The molecules are arranged in a pseudo hexagonal rod packing with medium-strong hydrogen bonds and π-stacking. The antiferroelectric arrangement of neighbored rods leads to an averaging of the net dipolar moment in the whole crystal.