title: Origins of dihydrogen binding to metal-inserted porphyrins: electric polarization and Kubas interaction.
abstract: Using density functional theory calculations, we have investigated the interactions between hydrogen molecules and metalloporphyrins. A metal atom, such as Ca or Ti, is introduced for incorporation in the central N(4) cavity. Within local density approximation (generalized gradient approximation), we find that the average binding energy of H(2) to the Ca atom is about 0.25 (0.1) eV/H(2) up to four H(2) molecules, whereas that to the Ti atom is about 0.6 (0.3) eV per H(2) up to two H(2) molecules. Our analysis of orbital hybridization between the inserted metal atom and molecular hydrogen shows that H(2) binds weakly to Ca-porphyrin through a weak electric polarization in dihydrogen, but is strongly hybridized with Ti-porphyrin through the Kubas interaction. The presence of d orbitals in Ti may explain the difference in the interaction types.
authors.affiliation: Department of Physics, Graphene Research Institute and Institute of Fundamental Physics, Sejong University, Seoul 143-747, Korea.
authors.forename: Junga
authors.initials: J
authors.lastname: Ryou
authors.forename: Gunn
authors.initials: G
authors.lastname: Kim
authors.forename: Suklyun
authors.initials: S
authors.lastname: Hong
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D014025:Titanium / Q000737:chemistry*
chemical_list: D008665:Metalloporphyrins; D006859:Hydrogen; D014025:Titanium; D002118:Calcium