view article
Figure 1
The three triclinic polymorphs of iron pyrophosphate. (a) α3, high-temperature triclinic polymorph; (b) α2, room-temperature triclinic polymorph, modulated structure; (c) α1, low-temperature triclinic polymorph. Note how the segregation between long and short Fe—O bonds gets progressively more pronounced as the temperature decreases. The concomitant deviation of the O—P—O angle from 180° that allows this degree of freedom is less obvious, but still discernible. Bonds longer than 2.5 Å have been highlighted by broken lines. While this limit is arbitrary, it is notable that in the α2 and α1 polymorphs there are no Fe—O bonds in the range 2.3–2.8 Å.

IUCrJ
Volume 12| Part 6| November 2025| Pages 635-636
ISSN: 2052-2525
https://doi.org/10.1107/S2052252525009030