The average framework strain for the ZnCl 2 systems (∆E av MOF =16.74 kJ/mol) is larger than for the ZnI 2 systems (∆E av MOF =11.41 kJ/mol). * There are several factors which could have caused this: the size of the guest molecules in the pores, and the overall unit cell and therefore pore size. In this study, the average molecular weight of guest molecules in ZnCl 2 structures (296.8 g/mol) is larger than in ZnI 2 structures (245.0 g/mol). The average unit cell sizes of ZnCl 2 systems is also larger than ZnI 2 systems, at 14,335.1 Å 3 and 15,793.9 Å 3 , respectively. While the increased strain in the ZnCl 2 frameworks could simply be due to the larger molecules present in the pores, accounting for the average unit cell sizes of the ZnCl 2 and ZnI 2 structures indicates that the higher ∆E av MOF of ZnCl 2 systems is affected by a combination of factors. The reduced pore size of the ZnCl 2 system results in greater distortion of the framework to accommodate the overall larger guest molecule size, ultimately leading to higher framework strain.