To further assess flexibility, it was attempted to swell 1as by solvent exchange with water, which had previously produced the most open form of MIL-88A(Fe) (V = 2110 Å 3 ). PXRD analysis of a sample of 1as soaked in water at room temperature for one hour showed significant swelling, with a Pawley refinement giving a unit cell volume of 2410( ) Å 3 (SI, Figure ). This suggests that, should a closed pore sample be accessible, 1 has a potentially greater amplitude of flexibility than MIL-88A(Fe), likely due to the increased ionic radius of Sc 3+ compared to Fe 3+ . Relationships between the lengths of the crystallographic axes and unit cell volume for samples of 1 have been plotted against those previously reported for solvated MIL-88A(Fe) samples, further demonstrating the effect of ionic radius on the breathing behaviours of the two isostructural MOFs (Figure ). ) compared to data previously published for MIL-88A(Fe) from ref [9]. Data are tabulated in the SI, Table .