Frequency of Z ' values in organic and organometallic crystal structures

The frequencies of Z' values (formula units per asymmetric crystal unit) ar e documented for organic and organometallic crystal structures, using the C ambridge Structural Database. The absolute frequencies of all Z' values rep orted, relative frequencies for certain substance classes, the seven crysta l 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%).