Assembly of high-valent oxomanganese clusters in aqueous solution. Redox equilibrium of water-stable Mn3O4 4+ and Mn2O2 3+ complexes

Joseph E. Sarneski, H. Holden Thorp, Gary W Brudvig, Robert H. Crabtree, Gayle K. Schulte

Research output: Contribution to journalArticle

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Abstract

The aqueous chemistry of a binuclear mixed-valence cluster, [(bpy)2Mn(O)2Mn(bpy)2](ClO4) 3 (1), has been investigated. The cluster exists in a pH-dependent equilibrium with a higher valent trinuclear species, [Mn3O4(bpy)4(OH2)2] 4+ (2). The trinuclear cluster is favored at low pH, conditions that favor disproportionate of 1. Evaporation of a pH 1.9 solution of 1 leads to the precipitation of red crystals of 2 in the space group P1̄ with a = 14.902 (5) Å, b = 15.787 (5) Å, c = 12.676 (4) Å, α = 100.22 (2)°, β = 93.45 (3)°, and γ = 73.98 (3)°. A total of 3718 unique data with I ≥ 3(σ)I were refined to values of R and Rw of 8.3 and 11.3%, respectively. The temperature-dependent magnetic susceptibility shows strong antiferromagnetic coupling with (ℋ = J(S1·S2) + J'(S1·S3 + S2·S3)) g = 1.97, J = 182, cm-1, and J' = 98 cm-1. The S = 1/2 ground state gives a 35-line EPR spectrum with (from simulation) g = 1.965, A3 = 0.0066 cm-1, and A12 = 0.0061 cm-1. Electrochemistry and EPR show that the concentrations of 1 and 2 are governed by a pH-dependent equilibrium. At pH 2.5, 2 is the only species present in solution; at pH 6.5 only 1 is observable. Further, electrochemical reduction of 2 leads to the formation of 1 in aqueous solution and also in CH3CN. The relevance of this quantitative equilibrium to the photoactivated assembly of the manganese tetramer in photosystem II is discussed.

Original languageEnglish
Pages (from-to)7255-7260
Number of pages6
JournalJournal of the American Chemical Society
Volume112
Issue number20
Publication statusPublished - 1990

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Oxidation-Reduction
Paramagnetic resonance
Water
Photosystem II Protein Complex
Electrochemistry
Manganese
Magnetic susceptibility
Ground state
Evaporation
Crystals
compound A 12
Temperature
perchlorate
manganese oxide

ASJC Scopus subject areas

  • Chemistry(all)

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Assembly of high-valent oxomanganese clusters in aqueous solution. Redox equilibrium of water-stable Mn3O4 4+ and Mn2O2 3+ complexes. / Sarneski, Joseph E.; Thorp, H. Holden; Brudvig, Gary W; Crabtree, Robert H.; Schulte, Gayle K.

In: Journal of the American Chemical Society, Vol. 112, No. 20, 1990, p. 7255-7260.

Research output: Contribution to journalArticle

Sarneski, Joseph E. ; Thorp, H. Holden ; Brudvig, Gary W ; Crabtree, Robert H. ; Schulte, Gayle K. / Assembly of high-valent oxomanganese clusters in aqueous solution. Redox equilibrium of water-stable Mn3O4 4+ and Mn2O2 3+ complexes. In: Journal of the American Chemical Society. 1990 ; Vol. 112, No. 20. pp. 7255-7260.
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abstract = "The aqueous chemistry of a binuclear mixed-valence cluster, [(bpy)2Mn(O)2Mn(bpy)2](ClO4) 3 (1), has been investigated. The cluster exists in a pH-dependent equilibrium with a higher valent trinuclear species, [Mn3O4(bpy)4(OH2)2] 4+ (2). The trinuclear cluster is favored at low pH, conditions that favor disproportionate of 1. Evaporation of a pH 1.9 solution of 1 leads to the precipitation of red crystals of 2 in the space group P1̄ with a = 14.902 (5) {\AA}, b = 15.787 (5) {\AA}, c = 12.676 (4) {\AA}, α = 100.22 (2)°, β = 93.45 (3)°, and γ = 73.98 (3)°. A total of 3718 unique data with I ≥ 3(σ)I were refined to values of R and Rw of 8.3 and 11.3{\%}, respectively. The temperature-dependent magnetic susceptibility shows strong antiferromagnetic coupling with (ℋ = J(S1·S2) + J'(S1·S3 + S2·S3)) g = 1.97, J = 182, cm-1, and J' = 98 cm-1. The S = 1/2 ground state gives a 35-line EPR spectrum with (from simulation) g = 1.965, A3 = 0.0066 cm-1, and A12 = 0.0061 cm-1. Electrochemistry and EPR show that the concentrations of 1 and 2 are governed by a pH-dependent equilibrium. At pH 2.5, 2 is the only species present in solution; at pH 6.5 only 1 is observable. Further, electrochemical reduction of 2 leads to the formation of 1 in aqueous solution and also in CH3CN. The relevance of this quantitative equilibrium to the photoactivated assembly of the manganese tetramer in photosystem II is discussed.",
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T1 - Assembly of high-valent oxomanganese clusters in aqueous solution. Redox equilibrium of water-stable Mn3O4 4+ and Mn2O2 3+ complexes

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AU - Schulte, Gayle K.

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N2 - The aqueous chemistry of a binuclear mixed-valence cluster, [(bpy)2Mn(O)2Mn(bpy)2](ClO4) 3 (1), has been investigated. The cluster exists in a pH-dependent equilibrium with a higher valent trinuclear species, [Mn3O4(bpy)4(OH2)2] 4+ (2). The trinuclear cluster is favored at low pH, conditions that favor disproportionate of 1. Evaporation of a pH 1.9 solution of 1 leads to the precipitation of red crystals of 2 in the space group P1̄ with a = 14.902 (5) Å, b = 15.787 (5) Å, c = 12.676 (4) Å, α = 100.22 (2)°, β = 93.45 (3)°, and γ = 73.98 (3)°. A total of 3718 unique data with I ≥ 3(σ)I were refined to values of R and Rw of 8.3 and 11.3%, respectively. The temperature-dependent magnetic susceptibility shows strong antiferromagnetic coupling with (ℋ = J(S1·S2) + J'(S1·S3 + S2·S3)) g = 1.97, J = 182, cm-1, and J' = 98 cm-1. The S = 1/2 ground state gives a 35-line EPR spectrum with (from simulation) g = 1.965, A3 = 0.0066 cm-1, and A12 = 0.0061 cm-1. Electrochemistry and EPR show that the concentrations of 1 and 2 are governed by a pH-dependent equilibrium. At pH 2.5, 2 is the only species present in solution; at pH 6.5 only 1 is observable. Further, electrochemical reduction of 2 leads to the formation of 1 in aqueous solution and also in CH3CN. The relevance of this quantitative equilibrium to the photoactivated assembly of the manganese tetramer in photosystem II is discussed.

AB - The aqueous chemistry of a binuclear mixed-valence cluster, [(bpy)2Mn(O)2Mn(bpy)2](ClO4) 3 (1), has been investigated. The cluster exists in a pH-dependent equilibrium with a higher valent trinuclear species, [Mn3O4(bpy)4(OH2)2] 4+ (2). The trinuclear cluster is favored at low pH, conditions that favor disproportionate of 1. Evaporation of a pH 1.9 solution of 1 leads to the precipitation of red crystals of 2 in the space group P1̄ with a = 14.902 (5) Å, b = 15.787 (5) Å, c = 12.676 (4) Å, α = 100.22 (2)°, β = 93.45 (3)°, and γ = 73.98 (3)°. A total of 3718 unique data with I ≥ 3(σ)I were refined to values of R and Rw of 8.3 and 11.3%, respectively. The temperature-dependent magnetic susceptibility shows strong antiferromagnetic coupling with (ℋ = J(S1·S2) + J'(S1·S3 + S2·S3)) g = 1.97, J = 182, cm-1, and J' = 98 cm-1. The S = 1/2 ground state gives a 35-line EPR spectrum with (from simulation) g = 1.965, A3 = 0.0066 cm-1, and A12 = 0.0061 cm-1. Electrochemistry and EPR show that the concentrations of 1 and 2 are governed by a pH-dependent equilibrium. At pH 2.5, 2 is the only species present in solution; at pH 6.5 only 1 is observable. Further, electrochemical reduction of 2 leads to the formation of 1 in aqueous solution and also in CH3CN. The relevance of this quantitative equilibrium to the photoactivated assembly of the manganese tetramer in photosystem II is discussed.

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