# Free refined value in Rietveld

I have a question about Rietveld refinement

The author of this paper claimed that the free refined CN ligand is 1.081. However, they does not show how they got that number. They stated it was based from this table however I am not sure how you can get 1.081 from this table. What is the calculation?

Thank you.

Source:

### Reference

1. Wang, W.; Gang, Y.; Hu, Z.; Yan, Z.; Li, W.; Li, Y.; Gu, Q.-F.; Wang, Z.; Chou, S.-L.; Liu, H.-K.; Dou, S.-X. Reversible Structural Evolution of Sodium-Rich Rhombohedral Prussian Blue for Sodium-Ion Batteries. Nature Communications 2020, 11 (1), 980. DOI: 10.1038/s41467-020-14444-4
• "they does not show how they got that number"—Well, they kinda do, it's just that you don't have raw data to follow it: "All PXRD data analysis was done in TOPAS 5 software. The PXRD data was first indexed to get unit cell, lattice parameters, and crystal symmetry information. Then the indexed unit cell was used for Le Bail fitting the PXRD data to derive the suitable peak profile, and lattice parameters. These derived data was fixed and used for further Rietveld refinement." – andselisk Dec 30 '20 at 12:27

• I would highly doubt that $d(\ce{C#N})$ can be as small as 1.081 Å (typical nitrile bond is 1.16 Å), that's more likely $d(\ce{C-H}).$ Besides, if you read the paper, it explicitly says that 1.081 is the site occupancy of free refined CN ligand before they fixed occupancies for carbon and nitrogen atoms at 100%. I do agree though regarding your point on VESTA, this is wonderful piece free of software, but here it won't help to get this number. Raw data + TOPAS 5, like authors did, is probably the only way. – andselisk Dec 30 '20 at 12:21