Density functional study on metal decoration onto a metal-organic framework

We carried out density functional theory calculations on the adsorption of a Ti atom at the Zn-O3, Zn-O2 and Hex sites in one of isoreticular metal-organic frameworks (IRMOFs). The binding energy is largest at the Hex site and smallest at the Zn-O3 site. Through the analyses of the orbitals and then density of states plots, we also found that the binding at the Hex site was due to direct orbital overlap between the Ti atom and the carbon atoms of the phenyl ring. When a Ti atom binds to the Zn-O3 site, the interactions of the d orbitals of the Ti atom with the adjacent oxygen atoms have anti-bonding characters. At the Zn-O2 site, however, the d orbitals of the Ti atom have bonding interactions with the oxygen atoms of the carboxylate groups. Thus, the binding energy is larger at the Zn-O2 site than at the Zn-O2 site.