The Crystallographic Interchange File (CIF) format is increasingly used for data transfer - and some journals now provide templates for authors to complete when submitting data with their manuscripts.
Although sometimes touted as a "human-readable" format, the CIF format is actually quite complex, and if errors are to be avoided, users should be aware of the detailed formatting rules. CrystalMaker is quite fussy in this regard because, unlike many other programs, CrystalMaker can parse different text formats "on the fly", auto-detecting the file type and generating structures, bonds and polyhedra automatically.
1. Data tags with no matching data item(s). Each CIF data tag (the string beginning with an "_" underscore character) must have a data item (either a number or a character string) associated with it, e.g.,
| _publ_requested_coeditor_name | Wrong! | |
| _publ_requested_coeditor_name | ? | ok |
| _publ_requested_coeditor_name | 'joe bloggs' | ok |
2. Data strings not correctly delimited. Strings containing spaces are interpreted as multiple items, unless they are enclosed within quotes (for a string on a single line) or semicolons (multi-line string), e.g.,
| _publ_requested_journal | J. Am. Chem. Soc. | Wrong! |
| _publ_requested_journal | 'J. Am. Chem. Soc.' | ok |
| _publ_contact_author Dr B A D Cif University of Somewhere Big City Neverland |
Wrong! Multi-line string needs to be delimited. |
| _publ_contact_author ; Dr O K Cif University of Somewhere Big City Neverland ; |
ok |
3. Loops with no data tags and/or data items. Each cif loop_ construct must be followed by one or more data tags, followed by a series of data items, e.g.,
| loop_ 'x, y, z' '-x, -y, -z' |
Wrong! No data tag |
| loop_ _symmetry_equiv_pos_as_xyz 'x, y, z' '-x, -y, -z' |
ok |
4. Loops with inconsistent data tags and/or data items. The number of data items must be an exact multiple of the number of data tags, e.g.,
| loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z O1 0.1786 0.40597 0.90810 O2 0.2138 0.14537 0.39271 Uij O3 0.1552 0.17296 |
Wrong! Extra data item for 'O2' line; missing item at line 'O3' |
| loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z O1 0.1786 0.40597 0.90810 O2 0.2138 0.14537 0.39271 O3 0.1552 0.03600 0.17296 |
ok |
The International Union of Crystallography (IUCr), which has developed the CIF format, provides a free CIF Validation Service. We strongly recommend that regular CIF users try out this program.
See Also