Solvent exchange was therefore utilised to attempt to access a fully closed sample of 1. Samples of 1as were soaked in different solvents for 7 days and were exchanged with fresh solvent, before being dried overnight in a vacuum desiccator and subsequently analysed by PXRD (SI, Section S4). The dynamic behaviour of 1 is evident in PXRD patterns collected following solvation and subsequent evacuation, whereby the framework contracts to various degrees dependent on solvent. The diffractograms again show broad Bragg reflections suggesting anisotropic breathing and making indexing difficult. Density functional theory (DFT) calculations were therefore utilised to attempt to interpret the diffraction data, and a closed structural model of 1, termed 1cp-sim, was generated (SI, Section S4). First, the open-pore structure of 1 was computationally optimised by DFT, and then further optimised under pressure, which forced the structure to undergo the open to closed phase transformation. Subsequently, the now closed-pore structure was re-optimised under ambient pressure to obtain the lattice parameters of the closed-pore structure under ambient pressure, 1cpsim. The unit cell volume (V = 1123 Å 3 ) is very close to that previously determined for MIL-88A(Fe) (V = 1135 Å 3 ), showing its validity. To interpret the experimental powder-X-ray diffraction data, a range of structures of 1 with different unit cell volumes (i.e. at different levels of closing) was generated.