A Mn-15 single-molecule magnet consisting of a supertetrahedron incorporated in a loop
Résumé
Two new Mn-15 clusters consisting of a supertetrahedron which is incorporated in a loop are reported. The reactions of [Mn(O2CEt)(2)]center dot 2H(2)O with the diols 1,3-propanediol (H(2)pd) or 2-methyl-1,3-propanediol (H(2)mpd) in the presence of KX (X = CN-, Cl-, Br-, NO3-, ClO4-, OCN-, SCN-) afforded compounds [Mn15K(mu(4)-O)(4)(O2CEt)(11)(pd)(12)(py)(2)] (1) and [Mn15K(mu(4)-O)(4)(O2CEt)(11)(mpd)(12)(py)(2)] (2). The structural core of 1 and 2 consists of a Mn-11 loop and a Mn9K supertetrahedron sharing a Mn-5 triangle. To the best of our knowledge, the structural motif of a supertetrahedron incorporated in a loop appears for the first time in metal cluster chemistry. Variable-temperature, solid-state direct current (dc) magnetic susceptibility studies in the 300-5 K range showed that the chi T-M value increases with decreasing T suggesting the existence of predominant ferromagnetic exchange interactions and a relatively large ground state spin. This was confirmed by field-variable temperature magnetization measurements which were fitted using a matrix diagonalization method to give S similar to 23/2, g = 1.92(1) and D = -0.071(2) cm(-1). In addition, compound 1 displays frequency-dependent alternating current (ac) signals suggesting single-molecule magnetism (SMM) behaviour. This was proven by magnetization vs. dc field sweeps on single-crystals of 1 center dot 0.7py center dot 1.3MeCN, which displayed sweep rate- and temperature-dependent hysteresis loops