Frequency of Z' values in organic and organometallic crystal structures.

The frequencies of Z' values (formula units per asymmetric crystal unit) are documented for organic and organometallic crystal structures, using the Cambridge Structural Database. The absolute frequencies of all Z' values reported, relative frequencies for certain substance classes, the seven crystal systems and the most abundant space groups are given. The three Z' values 1/2, 1 and 2 make up 95.3% of all crystal structures. Structures with Z' > 1 occur most frequently with nucleosides and nucleotides (20.8%), and with steroids (18.8%).