Redox reactivity of bis(1,4,7-triazacyclononane)iron(II/III) complexes in alkaline solution and characterization of a deprotonated species: Amidoiron(III) vs aminyliron(II) ground-state formulation. EPR, kinetic, pulse radiolysis, and laser photolysis study. [Electrons]

Journal Article · Wed Feb 10 04:00:00 EST 1988 · Inorganic Chemistry; (USA)

DOI:https://doi.org/10.1021/ic00276a003· OSTI ID:5612633

Pohl, K; Wieghardt, K; Kaim, W; Steenken, S ^[1]

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1. Lehrstuhl fuer Anorganische Chemie I der Ruhr-Universitaet, Bochum (West Germany)

The redox reactivity of the low-spin complexes (FeL{sub 2}){sup 3+} and (FeL{sub 2}{sup 2+} (L = 1,4,7-triazacyclononane, C{sub 6}H{sub 15}N{sup 3}) in alkaline aqueous solution has been investigated. Orange (Fe{sup III}L{sub 2}){sup 3+} is reversibly deprotonated in alkaline solution to yield a deep blue species, which has been characterized by its frozen-solution EPR spectrum as the low-spin amidoiron(III) complex, (Fe{sup III}L(L-H)){sup 2+} (LL-H) is the N-deprotonated form of the ligand L). The aminyl radical iron(II) formulation, (Fe{sup ii}l({sup .}L-H)){sup 2+}, is proposed to be an electronically excited state (ligand-to-metal charge transfer). (Fe{sup III}L(L-H)){sup 2+} disproportionates slowly under anaerobic conditions to yield 50% (Fe{sup II}L{sub 2}){sup 2+} and probably 50% (LFe{sup II}(OH{sub 2}){sub 3}){sup 2+} and a two-electron-oxidation product of one 1,4,7-triazacyclononane ligand, which has not been characterized. In the presence of an external oxidant (H{sub 2}O{sub 2} or oxygen) the blue species decomposes to produce quantitatively 1 equiv of oxidized macrocycle and (Fe{sup III}L(OH{sub 2}){sub 3}){sup 3+}. The kinetics of both reactions have been measured. Pulse radiolysis experiments have shown that the oxidation of (FeL{sub 2}){sup 2+} with Br{sub 2}{sup .{minus}}, I{sub 2}{sup .{minus}}, and (SCN){sub 2}{sup .{minus}} and oxygen-centered radicals such as OH{sup .} and the phenoxyl radical yield (Fe{sup III}L{sub 2}){sup 3+} at nearly diffusion controlled rates in the pH range 4-10. At higher pH values (11-13) the blue amidoiron(III) species is formed. (Fe{sup III}L(L-H)){sup 2+} oxidizes ascorbate(2{minus}) to give (Fe{sup II}L{sub 2}){sup 2+} and the ascorbate(1{minus}) radical. 51 refs., 8 figs., 2 tabs.

• OSTI ID: 5612633
• Journal Information: Inorganic Chemistry; (USA), Journal Name: Inorganic Chemistry; (USA) Journal Issue: 3 Vol. 27:3; ISSN 0020-1669; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400500 -- Photochemistry
400600* -- Radiation Chemistry
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELECTRON SPIN RESONANCE
ELECTRONS
ELEMENTARY PARTICLES
EXPERIMENTAL DATA
FERMIONS
HETEROCYCLIC COMPOUNDS
INFORMATION
IRON COMPLEXES
IRRADIATION
LASER RADIATION
LEPTONS
MAGNETIC RESONANCE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PULSED IRRADIATION
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
RADIOLYSIS
REDOX REACTIONS
RESONANCE
TRANSITION ELEMENT COMPLEXES