A mixed-valence metallogrid [Co III2Co II2] with an unusual electronic structure and single-ion-magnet characterization

Abstract

The reaction of the multisite coordination ligand (H₂L) with Co(Ac)₂·4H₂O in the absence of any base affords a homometallic tetranuclear mixed-valence complex, [Co₄(L)₄(CH₃CO₂)₂(CH₃OH)₂]·Et₂O (1). This mixed-valence metallogrid [Co₄(L)₄(CH₃CO₂)₂ (CH₃OH)₂]·Et₂O (1) has been theoretically and experimentally analyzed to assign the valence and spin state in the form of trans-[Co^III_ls–Co^II_hs–Co^III_ls–Co^II_hs]. HF-EPR reveals the presence of axial anisotropy (D = −34.4 cm⁻¹) with a significant transverse component (E = 9.5 cm⁻¹) in the local high spin cobalt centers. Slow magnetic relaxation effects were observed in the presence of a dc field, demonstrating field-induced single ion magnetic behavior, which is associated with the unusual electronic structure of Co(II) within the metallogrid.