As noted earlier, the equilibrium between FeDTPA2" and FeDTPA-OFI3" is slow and, therefore, it is unlikely that normal ligand exchange is involved. It is known that Fem can expand its coordination sphere from 6 to 7 and we might speculate that OH" occupies a coordination site that is otherwise available for attack by the DTPA radical.As pointed out previously, on the time scale of the experiment the DTPA radical has not quantitatively converted to its final form (generally considered as a methylene radical of an acetate group). However, it seems likely that we are dealing with a carbon-centered radical as the final form of the transient metal adduct, LFelnDTPAf*. Our data suggests a mechanism that involves an association, K6 -2.2 X 104 M"1 *, followed by a fast rearrangement, ki = 2.1 X 104 s"1, to a more stable form of the intermediate. The rate of reaction 7 excludes substitution processes but may be consistent with isomerization or tautomerization of the bound radical to its more stable form, albeit at a slightly higher rate than that of the corresponding process of the free DTPA radical (=H03 s"1).Decay of this species, LFemDTPAf", under all conditions that were experimentally accessible, involved a bimolecular reaction with excess FeDTPA2", indicating that the radical form liganded to the iron is insufficiently reducing to decay by intramolecular oxidation-reduction. The catalytic effect of a second FeDTPA2" on ligand oxidation may be analogous to that observed in other systems such as Cu"NTA.

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ABSTRACT:Photopolymerization of vinyl monomers sensitized by tris(2,2'-bipyridine)-ruthenium(II) complex was studied in polar solvents. No vinyl monomer tested was photopolymerized in the presence of sensitizer + alone under irradiation of visible light. Acrylamide (AA) was found to be photopolymerized in the presence of both the sensitizer and an electron donor triethylamine. The photopolymerization of AA did not occur in the presence of the sensitizer and methylviologen as an electron acceptor, but did in the coexistence of KSCN. In these systems the photosensitizer + was not consumed during the polymerization. The photopolymerization mechanisms for the +-sensitized systems are discussed.

In the electron-transfer reaction from the fluorescent intramolecular exciplexes of a copolymer containing phenanthrene and N,N-dimethylaniline moieties, and of a model compound to electron acceptors, the reactivity of the exciplexes was studied kinetically in polar and nonpolar media. The copolymer was poly(9-vinylphenanthrene-co-p-dimethylaminostyrene) and the model compound was N,N-dimethyl-4-[3-(9-phenanthryl)propyl]aniline. The oxidation potential of the exciplex was evaluated by the relation of the exciplex-quenching rate constants to the reduction potentials of electron-accepting quenchers according to the equations of Rehm and Weller. It was found that the electron-donating ability of these intramolecular exciplexes resembled with each other and was larger than that of excited phenanthrene. In polar media the donating ability was very close to that of the phenanthrene anion radical.

ABSTRACT:Photopolymerization of acrylamide (AA) sensitized by tris(l, I 0-phenanthroline )-ruthenium(II) and tris(2,2'-bipyrazine)ruthenium(II) complexes and was studied in aqueous solutions. AA was photopolymerized in the presence of both the sensitizer + and an electron donor triethylamine (TEA). The photopolymerization of AA did not occur in the presence of the sensitizer and TEA, but did in the coexistence of maleic acid as a comonomer. In these systems the Ru(II) complexes were not consumed during the polymerization. The mechanisms of photopolymerization for these systems are discussed.