A key aspect here is that bonds are covalent, hence strong and directional, and topologies are simple. Further, the reticular synthesis approach developed means that these materials can be designed on an aprioristic basis. In fact nowadays their number approaches one million.
That said, it may seem difficult to study MOF materials from a general viewpoint, and this is precisely one of the aims in our group. General principles may help to rationalise their properties and we start by adsorption of molecular hydrogen. The idea behind is the very old that hydrogen bonds unoccupied d-orbitals of metals. It is all not that simple, and several contributions have to be considered. Our approach is based on electronic-structure methods. We also wonder not only by the type of metal playing in the interaction but also by the shielding effect exerted by part of the organic ligand groups. The overal effect tends to be a weak physisorption and this deserves special attention from the point of view of the quantum-chemistry approach to be employed. Finally, considerations about the topology of the inorganic building units will be used in order to clarify ranges of adsorption energy that can be expected in these materials, together with considerations relating free volume with accessible surface area and density.
