Density Functional Theory Interpretation of the 1H Photo-Chemically Induced Dynamic Nuclear Polarization Enhancements Characterizing Photoreduced Polyazaaromatic Ru(II) Coordination Complexes.

The unprotonated and protonated monoreduced forms of the polyazaarom. Ru(II) coordination complexes [Ru(tap)3]2+ and [Ru(tap)2(phen)]2+ (tap = 1,4,5,8-tetraazaphenanthrene ; phen = 1,10-phenanthroline), i.e., [Ru(tap)3]·+, [Ru(tap)2(phen)]·+, [Ru(tap)2(tap-H)]·2+, and [Ru(tap)(tap-H)(phen)]·2+, were studied by D. Functional Theory (DFT). The electron spin d. of these radical cations, the isotropic Fermi-contact, and the anisotropic dipolar contributions to the hyperfine coupling consts. of the H nuclei were calcd. in vacuo and using a continuum model for H2O 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 d. in the vicinity of tap H-2 and tap H-7 (the H atoms in the ortho position of the tap nonchelating N atoms). These results are in full agreement with recent steady-state 1H photo-Chem. Induced Dynamic Nuclear Polarization (photo-CIDNP) measurements. The DFT calcns. performed for the protonated species also predict major 1H photo-CIDNP enhancements at these positions. 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 expts. [on SciFinder(R)]