Intensity (arb.) Although these calculations show that both structures are equally thermodynamically stable, only one crystal structure has been reported experimentally. We suggest this could be due to the fact that the experimentally reported structure for desolvated B11 contains water molecules within the pores of the cage. The presence of these water molecules could stabilise P 3 relative to P 3c1, driving the crystalline phase behaviour. Moreover, the PXRD patterns of the two structures are very similar (Fig. )), containing many of the same reflections that only differ in intensity, and perhaps the two structures coexist in the bulk material where the relative alignment between layers of the cages is statistically distributed. This result is also seen in our simulations as for simulations with a larger value of J wa , where J wa = 25, the clusters contained more than three layers which resulted in a statistical distribution of the relative orientation of the cages between the layers (aligned or antialigned).