An oximate-based hexanuclear mixed-valence MnIII4MnII2 edge-sharing bitetrahedral core with an St = 5 spin ground state

Abstract

The synthesis, structures and magnetic properties of two hexanuclear Mn₆ clusters are reported: Mn₆(μ₄-O)₂(dapdo)₂(dapdoH)₄(μ₂-OH)₂](ClO₄)₂·6MeCN (1·6MeCN) and [Mn₆(μ₄-O)₂(dapdo)₂(dapdoH)₄(μ₂-OCH₃)₂](ClO₄)₂·2Et₂O (2·2Et₂O) [dapdo²⁻ is the dianion of 2,6-diacetylpyridine dioxime and dapdoH⁻ is the monoanion of the aforesaid dioxime ligand]. Both complexes are mixed-valent with two Mn^II and four Mn^III atoms disposed in an edge-sharing bitetrahedral core. Both complexes 1 and 2 display the same [Mn^III₄Mn^II₂(μ₄-O)₂(μ₂-OR)₂]¹⁰⁺ core in which R = H for 1 and R = Me for 2. The [Mn^III₄Mn^II₂] core is rather uncommon compared to the reported [Mn^III₂Mn^II₄] core in the literature. DC magnetic susceptibility measurements on 1 and 2 reveal the presence of competing exchange interactions resulting in an S_t = 5 ground spin state. The magnetic behavior of the compounds indicates antiferromagnetic coupling between the manganese(III) centers, whereas the coupling between the manganese(III) and manganese(II) is weakly antiferromagnetic or ferromagnetic depending on the bridging environments. Finally the interaction between the manganese(II) centers from the two fused tetrahedra is weakly ferromagnetic in nature stabilizing S_t = 5 ground spin state in compounds 1 and 2.