Preparation and properties of models for the photosynthetic water oxidation center: Spin frustration in the (Mn sub 4 O sub 2 (O sub 2 CR) sub 7 (pic) sub 2 ) sup minus anion

Journal Article · Wed Sep 04 00:00:00 EDT 1991 · Inorganic Chemistry; (United States)

DOI:https://doi.org/10.1021/ic00018a019· OSTI ID:7265595

Libby, E; Folting, K; Christou, G ^[1]; McCusker, J K; Schmitt, E A; Hendrickson, D N ^[2]

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1. Indiana Univ., Bloomington (United States)
2. Univ. of California, San Diego, La Jolla (United States)

Synthetic procedures are described that allow access to complexes containing the anion (Mn{sub 4}O{sub 2}(O{sub 2}CR){sub 7}(pic){sub 2}){sup {minus}} (R = Me, Et, Ph; picH = picolinic acid). Reaction mixtures consisting of Mn(O{sub 2}CR){sub 2} (R = Me, Ph), RCOOH, pic{sup {minus}}, and NBu{sup n}{sub 4}MnO{sub 4} in MeCN give deep red solutions from which the products (NBu{sup n}{sub 4})(Mn{sub 4}O{sub 2}(O{sub 2}CMe){sub 7}(pic){sub 2}) (1) and (NBu{sup n}{sub 4})(Mn{sub 4}O{sub 2}(O{sub 2}CPh){sub 7}(pic){sub 2}) (2) can be obtained in high yield and purity. The structure of the anion consists of an (Mn{sub 4}({mu}{sub 3}-O){sub 2}){sup 8+} core with the four Mn atoms disposed in a butterfly' arrangement and O atoms triply bridging each plane ( wing'). Peripheral ligation is provided by seven {mu}-AcO{sup {minus}} and two chelating pic{sup {minus}} groups; the overall structure has idealized C{sub 2} symmetry. The anion of 1 bears striking similarity to the cation (Mn{sub 4}O{sub 2}(O{sub 2}CMe){sub 7}(bpy){sub 2}){sup +} reported previously, showing little structural consequence of the pic-for-bpy substitution. Treatment of (Mn{sub 3}O(O{sub 2}CR){sub 6}(py){sub 3})(ClO{sub 4})(R = Me, Et) with Na(pic){center dot}{sup 3}/{sub 4}H{sub 2}O in MeCN leads to formation of sparingly soluble Na(Mn{sub 4}O{sub 2}(O{sub 2}CR){sub 7}(pic){sub 2}) salts, providing an additional synthetic route to the tetranuclear anions. Complex 1 can be cleanly converted to 2 by treatment with excess PhCOOH in MeCN, demonstrating facile carboxylate exchange with more acidic acids. Variable-temperature, solid-state magnetic susceptibility studies have been performed on complex 1 in the range 5-300 K. The spin frustration present in these (Mn{sub 4}O{sub 2}){sup 8+} complexes is examined. Depending on the magnitudes of J{sub wb} and J{sub bb}, different ground states are found. The proton NMR spectra are reported for complex 1 in CDCl{sub 3}, CD{sub 3}CN, and (CD{sub 3}){sub 2}SO.

• OSTI ID: 7265595
• Journal Information: Inorganic Chemistry; (United States), Vol. 30:18; ISSN 0020-1669
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
MANGANESE COMPLEXES
CHEMICAL PREPARATION
MOLECULAR STRUCTURE
ACETONITRILE
ANIONS
BENZOIC ACID
CARBOXYLIC ACIDS
CHELATING AGENTS
FERROCENE
MAGNETIC SUSCEPTIBILITY
NMR SPECTRA
OXIDATION
PHOTOSYNTHESIS
REDOX REACTIONS
TEMPERATURE RANGE 0000-0013 K
TEMPERATURE RANGE 0013-0065 K
TEMPERATURE RANGE 0065-0273 K
VOLTAMETRY
WATER
CHARGED PARTICLES
CHEMICAL REACTIONS
COMPLEXES
DIENES
HYDROCARBONS
HYDROGEN COMPOUNDS
IONS
IRON COMPLEXES
MAGNETIC PROPERTIES
MONOCARBOXYLIC ACIDS
NITRILES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHYSICAL PROPERTIES
POLYENES
SPECTRA
SYNTHESIS
TEMPERATURE RANGE
TRANSITION ELEMENT COMPLEXES
400500* - Photochemistry
400201 - Chemical & Physicochemical Properties