pubs.acs.org
Close Enough: Approximate Symmetry in Recent Crystal Structures with Extreme Z′ (Z′ ≥ 12)
To further highlight the link between approximate symmetry and homomolecular structures that crystallize with large numbers of molecules in the asymmetric unit (Z′ ≥ 12), the most recent structures of this type have been analyzed, and the approximate symmetry identified. In most cases, when approximate symmetry is considered, a smaller approximate unit cell can be described, where the effective Z′ is lower than that of the original unit cell. For one example, defining an approximate cell was not appropriate, and the approximate symmetry in the structure was hence described using approximate layer and rod groups. Generally, it appears that though the molecules in the asymmetric units of these structures may not be related by crystallographic symmetry, symmetrical relationships appear to be retained as much as possible in cases where the packing is awkward and precise symmetry is not possible. Revealing the link between extreme-Z′ structures and theoretical structures with lower Z′ is of potential use to the field of crystal structure prediction with regard to the prediction of structures where Z′ > 1.
