London Dispersion Governs the Interaction Mechanism of Small Polar and Non-Polar Molecules in Metal-Organic Frameworks

In this work we investigate the adsorption of chlorinated methanes (CH_xCl_4-x, x=0-4) in a representative layer-pillar Metal-Organic Framework (MOF), the flexible MOF Ni₂(ndc)₂(dabco) (ndc = 2,6-naphthalene-dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane), also known as DUT-8(Ni). The guest molecules show a systematic increase of polarizability with increasing number of chlorine atoms, while the dipole moment exceeds 2 Debye for x = 2 and 3. Our ligand field molecular mechanics (LFMM) simulations show that, counter-intuitively, the host-guest interactions are mainly characterized by London dispersion, despite the molecular dipole moments reaching magnitudes as large as water. This highlights the importance of London dispersion interactions in the description of host-guest interactions.