∆E MOF is on the same order of magnitude as for single molecules, indicating that breathing of the framework does not come at a large energetic penalty. Furthermore, guest exchange does not cause significant amounts of distortion in the framework: the change in cell volume between the optimised experimental structure and the optimised empty framework is typically less than 3%. This exhibits the breathing capabilities of the framework that occurs during the thermodynamic guest exchange process, and does not appear to correlate with framework strain (Fig. ).