The strain energy of the MOF was also quantified to provide insight into the distortion of the framework that occurs on uptake of the guest molecule. All guest and solvent molecules were removed from the optimised CS structure, leaving the empty (ZnX 2 ) 3 (tpt) 2 framework. The energy of the MOF in the op-timised CS structure E crystal MOF was calculated by running a single point energy calculation of the empty framework. An unconstrained geometry optimisation was also performed on the empty MOF structure, applying the same calculation settings as described above. The energy difference between the single-point and relaxed empty MOF structures (E