title: Binuclear manganese compounds of potential biological significance. 1. Syntheses and structural, magnetic, and electrochemical properties of dimanganese(II) and -(II,III) complexes of a bridging unsymmetrical phenolate ligand.
abstract: Reactions of the unsymmetrical phenol ligand 2-(bis(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomethyl)-4-methylphenol with Mn(OAc)(2).4H(2)O or Mn(H(2)O)(6)(ClO(4))(2) in the presence of NaOBz affords the dimanganese(II) complexes 1(CH(3)OH), [Mn(2)(L)(OAc)(2)(CH(3)OH)](ClO(4)), and 2(H(2)O), [Mn(2)(L)(OBz)(2)(H(2)O)](ClO(4)), respectively. On the other hand, reaction of the ligand with hydrated manganese(III) acetate furnishes the mixed-valent derivative 3(H(2)O), [Mn(2)(L)(OAc)(2)(H(2)O)](ClO(4))( 2). The three complexes have been characterized by X-ray crystallography. 1(CH(3)OH) crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.9215(6) A, b = 20.2318(12) A, c = 19.1354(12) A, alpha = 90 degrees, beta = 97.5310(10) degrees, gamma = 90 degrees, V = 4191.7 A(3), and Z = 4. 2(H(2)O) crystallizes in the monoclinic system, space group P2(1)/n, with a = 10.9215(6) A, b = 20.2318(12) A, c = 19.1354(12) A, alpha = 90 degrees, beta = 97.5310(10) degrees, gamma = 90 degrees, V = 4191.7 A(3), and Z = 4. 3(H(2)O) crystallizes in the monoclinic system, space group P2(1)/c, with a = 11.144(6) A, b = 18.737(10) A, c = 23.949(13) A, alpha = 90 degrees, beta = 95.910(10) degrees, gamma = 90 degrees, V = 4974(5) A(3), and Z = 4. Magnetic measurements revealed that the three compounds exhibit very similar magnetic exchange interactions -J = 4.3(3) cm(-)(1). They were used to establish tentative magneto-structural correlations which show that for the dimanganese(II) complexes -J decreases when the Mn-O(phenoxo) distance increases as expected from orbital overlap considerations. For the dimanganese(II,III) complexes, crystallographic results show that the Mn(II)-O(phenoxo) and Mn(III)-O(phenoxo) bond lengths are inversely correlated. An interesting magneto-structural correlation is found between -J and the difference between these bond lengths, delta(Mn)(-)(O) = d(Mn)()II(-)(O) - d(Mn)()III(-)(O): the smaller this difference, the larger -J. Electrochemical studies show that the mixed-valence state is favored in 1-3 by ca. 100 mV with respect to analogous complexes of symmetrical ligands, owing to the asymmetry of the electron density as found in the analogous diiron complexes.
authors.affiliation: Laboratoire de Physicochimie des Métaux en Biologie, FRE 2427, CEA-CNRS-UJF, Département Réponse et Dynamique Cellulaires, CEA-Grenoble, 38054 Grenoble Cedex 9, France.
authors.forename: Lionel
authors.initials: L
authors.lastname: Dubois
authors.forename: Dao-Feng
authors.initials: DF
authors.lastname: Xiang
authors.forename: Xian-Shi
authors.initials: XS
authors.lastname: Tan
authors.forename: Jacques
authors.initials: J
authors.lastname: Pécaut
authors.forename: Peter
authors.initials: P
authors.lastname: Jones
authors.forename: Stéphane
authors.initials: S
authors.lastname: Baudron
authors.forename: Laurent
authors.initials: L
authors.lastname: Le Pape
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Latour
authors.forename: Carole
authors.initials: C
authors.lastname: Baffert
authors.forename: Sylvie
authors.initials: S
authors.lastname: Chardon-Noblat
authors.forename: Marie-Noëlle
authors.initials: MN
authors.lastname: Collomb
authors.forename: Alain
authors.initials: A
authors.lastname: Deronzier
mesh_terms: D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D010636:Phenols / Q000138:chemical synthesis*; D013696:Temperature
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D008345:Manganese