title: A synthetic strategy for a new series of oxo-centered tricobalt complexes with mixed bridging ligands of acetate and pyrazolate anions.
abstract: A new series of oxo-centered tricobalt(III, III, III) complexes, containing mixed bridges of acetate and pyrazolate anions, has been synthesized based on a strategy consisting of two stages. In the first stage, the reaction of cobalt(II) acetate tetrahydrate with pyrazole in the presence of oxidants, followed by purification with silica-gel column chromatography, afforded six tricobalt complexes: [Co(3)O(μ-OAc)(5)(μ-pz)(Hpz)(3)](PF(6)) (mono), two isomers of [Co(3)O(μ-OAc)(4)(μ-pz)(2)(Hpz)(3)](PF(6)) (bis-1 and bis-2), two isomers of [Co(3)O(μ-OAc)(3)(μ-pz)(3)(Hpz)(3)](PF(6)) (tris-2 and tris-3), and one isomer of [Co(3)O(μ-OAc)(2)(μ-pz)(4)(Hpz)(3)](PF(6)) (tetra-1). In the second stage, substitution reactions have been examined for the complexes obtained in the first stage. As a result, one acetate bridge in bis-1, bis-2, and tris-3 could be substituted with one pyrazolate site-selectively. Bis-1, bis-2, and tris-3 were converted to another isomer of [Co(3)O(μ-OAc)(3)(μ-pz)(3)(Hpz)(3)](PF(6)) (tris-1), tris-2, and tetra-1, respectively. Single-crystal X-ray diffraction studies found that in every complex acetato and pyrazolato work as bridging ligands, while pyrazole (Hpz) acts as a terminal ligand. Moreover, the electrochemical properties of the seven new tricobalt complexes (mono, bis-1, bis-2, tris-1, tris-2, tris-3, and tetra-1) were investigated by cyclic voltammetry and it was found that (1) each complex shows reversible redox behaviour corresponding to the Co(III)Co(III)Co(III)/Co(III)Co(III)Co(IV) couple and (2) the redox potential decreases from 1.21 V vs. Fc/Fc(+) in mono to 1.09 V vs. Fc/Fc(+) in tetra-1, as the number of pyrazolate bridges increases.
authors.affiliation: Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan. yoshidaj@kitasato-u.ac.jp
authors.forename: Jun
authors.initials: J
authors.lastname: Yoshida
authors.forename: Shohei
authors.initials: S
authors.lastname: Kondo
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Yuge
mesh_terms: D000085:Acetates / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D055664:Electrochemical Techniques; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010084:Oxidation-Reduction; D011720:Pyrazoles / Q000737:chemistry*
chemical_list: D000085:Acetates; D000838:Anions; D008024:Ligands; D009942:Organometallic Compounds; D011720:Pyrazoles; D003035:Cobalt