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International
Tables for Crystallography Volume G Definition and exchange of crystallographic data Edited by J. R. Hester and B. McMahon © International Union of Crystallography 2026 |
International Tables for Crystallography (2026). Vol. G. Early view chapter
https://doi.org/10.1107/97809553602060001011 Chapter 4.2 Core dictionary (coreCIF) |
Core dictionary version 3.3.0
_cell.formula_units_Z_prime
Name:_cell.formula_units_Z_prime
Definition:
Z' specifies the number of molecules in the asymmetric unit.
It is defined as the number of formula units in the unit cell
(_cell.formula_units_Z) divided by the multiplicity of the
general position of the corresponding space group. Z' can be
a fraction or a positive integer.
Note that correct assignment of Z' may be difficult for some
complex structures (Flack, 2002; Steed et al., 2014). For such
cases a justification of the assigned value should be given in
_cell.formula_units_Z_prime_details.
References: Flack, H. D. (2002).
https://www.iucr.org/__data/iucr/lists/coredmg/msg00196.html
Steed, J. et al. (2014). https://zprime.co.uk/limitations
Examples:| 5 | Crystal structure contains five molecules in the asymmetric unit. One such crystal structure (tetraphenylphosphonium octahydrotriborate) is described by Beckett, M. A. et al. (2010). Acta Cryst. E66, o833. |
| 1.5 | Crystal structure contains one and a half instances of a molecule in the asymmetric unit. One such crystal structure [9-(methoxymethyl)anthracene] is described by Liu, J. et al. (2007). Acta Cryst. E63, o4442. |
| 0.5 | Crystal structure contains half of a molecule in the asymmetric unit. One such crystal structure [(E)-1,1,4,4-tetraphenylbut-2-yne-1,4-diol] is described by Sundar, J. K. et al. (2010). Acta Cryst. E66, o679. |
Type: Real
Units: none
The permitted range is 0 → infinity
Category:
cell
