Ab Initio Study of the Adsorption of Small Molecules on Metal-Organic Frameworks with Oxo-centered Trimetallic Building Units: The Role of the Undercoordinated Metal Ion

The interactions of H₂, CO, CO₂, and H₂O with the undercoordinated metal centers of the trimetallic oxo-centered M₃^III(μ₃-O)(X) (COO)₆ moiety are studied by means of wave function and density functional theory. This trimetallic oxo-centered cluster is a common building unit in several metal-organic frameworks (MOFs) such as MIL-100, MIL-101, and MIL-127 (also referred to as soc-MOF). A combinatorial computational screening is performed for a large variety of trimetallic oxo-centered units M₃^IIIO (M = Al³⁺, Sc³⁺, V³⁺, Cr³⁺, Fe³⁺, Ga³⁺, Rh³⁺, In³⁺, Ir³⁺) interacting with H₂O, H₂, CO, and CO₂. The screening addresses interaction energies, adsorption enthalpies, and vibrational properties. The results show that the Rh and Ir analogues are very promising materials for gas storage and separations.