Ferromagnetic manganese “cubes”: from PSII to single-molecule magnets

Abstract

The reaction of Mn(O₂CMe)₂·2H₂O with Me-saoH₂ (Me-saoH₂= 2-hydroxyphenylethanone oxime) in MeCN forms the complex [Mn^III₄(Me-sao)₄(Me-saoH)₄] (1) in good yields. Replacing Me-saoH₂ with Naphth-saoH₂ (Naphth-saoH₂ = 2-hydroxy-1-napthaldoxime) in the presence of CH₃ONa forms the complex [Mn^III₄(Naphth-sao)₄(Naphth-saoH)₄] (2) in low yields, while the reaction between Mn(ClO₄)₂·6H₂O, Et-saoH₂ (Et-saoH₂= 2-hydroxypropiophenone oxime) and NBu₄OH in MeCN gives the complex [Mn^III₄(Et-sao)₄(Et-saoH)₄] (3) in moderate yields. All three tetrametallic cages exclusively contain Mn^III centres arranged in a “cube”-like topology, in which the metal centres are connected by–N–O_oximate groups. The magnetic properties of 1–3 are near identical, revealing the presence of only ferromagnetic interactions between the metal ions leading to high-spin ground states of S = 8. The complexes display frequency dependent out-of-phase signals in ac susceptibility studies and, in the case of 1 single-molecule magnetism has been observed by means of single-crystal hysteresis loop measurements.