A new family of {Co₄Ln₈} metallacrowns with a butterfly-shaped structure

A series of cobalt–lanthanide metallacrowns (MCs) {Co^III₄Ln₈} (Ln = Dy³⁺1, Ho³⁺2 and Tm³⁺3) based on pyrazinehydroxamic acid (H₂pyzha) and pyrazinic acid (Hpyzic) ligands have been synthesized. These isomorphous 3d–4f MCs contain two novel [12-MC-4] with –[Co–N–O–Ln]– connectivity to capture one Ln³⁺ ion in the core of each MC. Two [12-MC-4] units are connected with the central Ln³⁺ ions forming a butterfly-shaped structure. The existence of this structure leads to a new coordination mode of H₂pyzha which has never previously been reported. The magnetic properties of these MCs have been studied and the {Co^III₄Dy₈} (1) was found to exhibit the single-molecule magnet (SMM) behavior.