As to be expected, each added chlorine atom increases the polarizability and therefore the amount of vdW interaction between the guests and between guest and MOF. From CH 4 to CCl 4 the decrease of E vdW is almost linear for both interactions. Only the CCl 4 contributions deviate slightly from a linear description. To investigate the accuracy of the guest-guest interactions in our simulations, we performed MP2 calculations (Def2QZVPP basis with counterpoise correction) on a CCl 4 and a CHCl 3 dimer (for details see Section 1.3 of the SI). No significant deviation of the interaction energies was found (less than 3 kJ mol -1 difference between MP2 and force field results, see also Section 3.9.1 of the SI). The Radial Distribution Functions (RDF) of carbons and chlorines in CCl 4 and CHCl 3 explain the slightly lower intermolecular interactions of CCl 4 in our simulations: The chlorine atoms in the CCl 4 simulations are a little further apart than the ones in the CHCl 3 simulations (see Figure ). We suggest two possible reasons: First, we only applied integer loadings of molecules, it is therefore not surprising that we did not observe an exact match of interatomic chlorine distances since the density relative to the size cannot be exactly matched using integer values of adsorbates. Secondly, CCl 4 does not have any dipole. It therefore misses a slightly attractive contribution that CHCl 3 does have.