Ferromagnetic manganese "cubes": from PSII to single-molecule magnets
Résumé
The reaction of Mn(O(2)CMe)(2)center dot 2H(2)O with Me-saoH(2) (Me-saoH(2) = 2-hydroxyphenylethanone oxime) in MeCN forms the complex [Mn(4)(III)(Me-sao)(4)(Me-saoH)(4)] (1) in good yields. Replacing Me-saoH(2) with Naphth-saoH(2) (Naphth-saoH(2) = 2-hydroxy-1-napthaldoxime) in the presence of CH(3)ONa forms the complex [Mn(4)(III)(Naphth-sao)(4)(Naphth-saoH)(4)] (2) in low yields, while the reaction between Mn(ClO(4))(2)center dot 6H(2)O, Et-saoH(2) (Et-saoH(2) = 2-hydroxypropiophenone oxime) and NBu(4)OH in MeCN gives the complex [Mn(4)(III)(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.