(hydrogen bonding) and blue rectangles. The wireframe view of the (110) and (

) faces emphasises the

molecules which have their mean planes perpendicular to the face. b A bent co-crystal of 1 with thickness of

~38 µm mounted for analysis. The blue arrow indicates the area covered by the mapping experiment and the

direction it was performed in. c Deformation graph of 1. Note that ε-..8/ is equivalent to ε(

due to

symmetry. The first dataset containing reflections is defined at 0 µm. For each data set the crystal was rotated

through a 30 ° wedge (15 ° either side of the centre). The beam was centred off the edges of the crystal, which is

~38 µm thick, at the start and end of the experiment. The centre of the crystal is located at ~ 19 µm. Some data

sets beyond 28 µm did not refine satisfactorily due to their position near the edge of the crystal and have been

Fig. 2 Proposed mechanism of elastic flexibility in co-crystals of 1. a The change in angle between the mean

plane of the hydrogen-bonded dimer and the (001) plane moving from the inside to the outside of the bend. b

Rotation compared to the (001) face and movement apart within the π-stack (d) facilitates the required cell

deformation. Δd = 0.04 Å, Δθ = 0.54 °. Disorder in the nitro-group is removed for clarity.