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Figure 1
Pressure dependence of the (a) unit-cell parameters and (b) volume. Full and empty symbols represent data for the compressed and decompressed crystal (where crystal structure was solved and refined), respectively. Data for the compressed/decompressed crystals where only unit-cell parameters were measured are marked with half-empty symbols (Table S2). Horizontal arrows in panel (b) of the figure mark pressure regions where each form of the crystal exists and pressure regions where C2/c and P21/c phases were observed (in purple and black, respectively). Orange–green gradient arrow marks the direction of the transformation from [{\rm BIPYH}_{2}^{2+}{\rm MA}^{2-}] to BIPYH+MA− in the P21/c phase. Vertical dashed and dashed-dotted lines mark the transition pressures pt and pt′ between the C2/c and P21/c phases on compression and decompression, respectively. Yellow highlight marks the pressure region where the BIPYMA/BIPYH+MA− interconversion can occur. The lines fitted to experimental points are guides to the eye only. Subscripts C and P stand for C2/c and P21/c, respectively.

IUCrJ
Volume 11| Part 2| March 2024| Pages 168-181
ISSN: 2052-2525
https://doi.org/10.1107/S2052252524000344