title: Density functional theory interpretation of the 1H photo-chemically induced dynamic nuclear polarization enhancements characterizing photoreduced polyazaaromatic Ru(II) coordination complexes.
abstract: The unprotonated and protonated monoreduced forms of the polyazaaromatic Ru(II) coordination complexes [Ru(tap)(3)](2+) and [Ru(tap)(2)(phen)](2+) (tap = 1,4,5,8-tetraazaphenanthrene ; phen = 1,10-phenanthroline), that is, [Ru(tap)(3)](*+), [Ru(tap)(2)(phen)](*+), [Ru(tap)(2)(tap-H)](*2+), and [Ru(tap)(tap-H)(phen)](*2+), were studied by Density Functional Theory (DFT). The electron spin density of these radical cations, the isotropic Fermi-contact, and the anisotropic dipolar contributions to the hyperfine coupling constants of the H nuclei were calculated in vacuo and using a continuum model for water solvation. For [Ru(tap)(2)(phen)](*+), as well as for its protonated form, the DFT results show that the unpaired electron is not localized on the phen ligand. For both [Ru(tap)(3)](*+) and [Ru(tap)(2)(phen)](*+), they reveal high electron spin density in the vicinity of tap H-2 and tap H-7 (the H atoms in the ortho position of the tap non-chelating N atoms). These results are in full agreement with recent steady-state (1)H photo-Chemically Induced Dynamic Nuclear Polarization (photo-CIDNP) measurements. The DFT calculations performed for the protonated species also predict major (1)H photo-CIDNP enhancements at these positions. Interestingly, they indicate significantly different polarization for tap H-9,10, suggesting that the occurrence of a photoinduced electron transfer with protonation of the reduced species might be detected by high-precision photo-CIDNP experiments.
authors.affiliation: Service de Chimie Quantique et Photophysique, CP 160/09, Université Libre de Bruxelles, 50 Avenue F.D. Roosevelt, B-1050 Bruxelles, Belgium.
authors.forename: Emilie
authors.initials: E
authors.lastname: Cauët
authors.forename: Stuart
authors.initials: S
authors.lastname: Bogatko
authors.forename: Epiphanie
authors.initials: E
authors.lastname: Mugeniwabagara
authors.forename: Luca
authors.initials: L
authors.lastname: Fusaro
authors.forename: Andrée
authors.initials: A
authors.lastname: Kirsch-De Mesmaeker
authors.forename: Michel
authors.initials: M
authors.lastname: Luhmer
authors.forename: Nathalie
authors.initials: N
authors.lastname: Vaeck
mesh_terms: D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010616:Phenanthrenes / Q000737:chemistry*; D010618:Phenanthrolines / Q000737:chemistry*; D055668:Photochemical Processes; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D010616:Phenanthrenes; D010618:Phenanthrolines; D012428:Ruthenium; C076699:ruthenium-tris-1,4,5,8-tetraazaphenanthrene; C025205:1,10-phenanthroline