Noncentrosymmetric (NCS) crystals exhibit a range of functional properties such as nonlinear optical activity, ferroelectricity, piezoelectricity, and pyroelectricity. One promising strategy to create NCS structures involves the use of racemic building block units containing a pair of enantiomers of both handedness. To better understand how to break inversion symmetry in racemic compounds, a computational approach was utilized to search the Cambridge Structural Database (CSD) for racemates crystallizing in achiral noncentrosymmetric crystal classes. A Python script was written to extract residue point group symmetry and other crystallographic information from deposited structures. The script was applied to the mm2, m, and 6bar2m crystal classes and out of 28,708, 14,725, and 261 structures, respectively, the script estimated that 2,327 (8%), 657 (4.5%), and 6 (2.4%) of the structures were racemates. A closer analysis of the 6bar2m class revealed that all racemates found shared similar crystal packing trends in which enantiomeric layers of organometallic residues were formed and related to each other by rotoinversion axes and mirror/glide planes to preclude the presence of inversion symmetry.

Computational search for achiral noncentrosymmetric racemates

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ACS Fall 2022

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