With the flexible 1 and the rigid 2 in hand, we sought to examine the effect of postsynthetic bromination of the fumarate linkers on the flexibility of both MOFs. Postsynthetic bromination reactions are often carried out on suspensions of the MOF in organic solvents, however, here we report the use of direct vapour diffusion to induce bromination, which we had previously used for postsynthetic iodination. While carrying out this work, a similar method was reported by Matemb Ma Ntep et al. to brominate acetylenedicarboxylate linkers in a Ce(IV) MOF. 1np and bromine liquid were added to separate, uncapped vials that were sealed in a closed vessel and allowed to react at room temperature for 48 hours in darkness (SI, Section S7). The resulting material, which we have termed 1-Br2, was subsequently washed in acetonitrile to remove excess bromine from the pores and dried at room temperature under vacuum for further analysis. Concurrently, single crystals of 1as