CIFs & Structure Factors: Improvements to Deposition & Request

​Experimental structure factor information is extremely important to the crystallographic community, both for the effective validation of crystal structures as well as the opportunity to revisit a refined model and attempt to extract more details from the data. The IUCr have led the way in this regard, with structure factor data requested and made available for their own journals since the mid-1990s. Since 2011, the IUCr has also recommended that publishers require authors to provide structure factors alongside any reported crystal structures to enable checking and archiving the data. At the same time the CCDC announced that structure factors would be accepted alongside Crystallographic Information Files (CIFs) for deposition to the Cambridge Structural Database (CSD).

It is now quite common for CIFs to include structure factor information embedded within them (rather than as separate HKL or FCF files) as well as some refinement details (e.g. the contents of RES files). This means that CIFs may be considerably larger in terms of file size compared to files without this extra embedded data. As part of our on-going efforts to make data deposition smoother and easier for contributors, we have now made it possible to upload a zipped folder of CIF, HKL and/or FCF files with a total size of up to 10MB. The CCDC Deposit a Structure webpage encourages both depositions relating to scientific publications as well as private communications of structures that are not intended for publication elsewhere.

3D molecular representation from a recently deposited organometallic crystal structure (CSD refcode UFOBEY) – in this case the CIF with embedded structure factors and refinement details was over 7MB in size

As the deposition of structure factors to the CSD is becoming much more common, we have also now provided a smoother mechanism for requesting this information through the CCDC Request a Structure webpage. Armed with either a CCDC deposition number or the DOI for the relevant publication, any user is now able to download a choice of the following; deposited CIFs with any embedded structure factor data included, deposited CIFs with any embedded structure factor stripped out or a zipped package of all the CIF(s) and any deposited structure factor files for the structure(s) in question.

Screenshot of the CCDC data request webpage with options for download formats including structure factors
We expect that the proportion of crystal structures deposited with structure factor data will continue to rise and hopefully at some point in the near future this will be the norm rather than the exception!