A new route for substitution of the bridging acetate on the oxo-centered triruthenium acetate cluster

Isolation of a Side-On V(III)-(η2-O2) through the Intermediacy of a Low-Valent V(II) in a Metal-Organic Framework

We report the isolation of vanadium(II) in a metal-organic framework (MOF) by the reaction of the chloride-capped secondary building unit in the all-vanadium(III) V-MIL-101 (1) with 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine. The reduced material, 2, has a secondary building unit with the formal composition [V^IIV₂^III], with each metal ion presenting one open coordination site. Subsequent reaction with O₂ yields a side-on η² vanadium-superoxo species, 3. The MOF featuring V(III)-superoxo moieties exhibits a mild enhancement in the isosteric enthalpy of adsorption for methane compared to the parent V-MIL-101. We present this synthetic methodology as a potentially broad way to access low-valent open metal sites within MOFs without causing a loss of crystallinity or porosity. The low-valent sites can serve as isolable intermediates to access species otherwise inaccessible by direct synthesis.

A synthetic strategy for a new series of oxo-centered tricobalt complexes with mixed bridging ligands of acetate and pyrazolate anions

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.