A Mn15 single-molecule magnet consisting of a supertetrahedron incorporated in a loop

Two new Mn15 clusters consisting of a supertetrahedron which is incorporated in a loop are reported. The reactions of [Mn(O2CEt)2]·2H2O with the diols 1,3-propanediol (H2pd) or 2-methyl-1,3-propanediol (H2mpd) in the presence of KX (X = CN−, Cl−, Br−, NO3−, ClO4−, OCN−, SCN−) afforded compounds [Mn15K(μ4-O)4(O2CEt)11(pd)12(py)2] (1) and [Mn15K(μ4-O)4(O2CEt)11(mpd)12(py)2] (2). The structural core of 1 and 2 consists of a Mn11 loop and a Mn9K supertetrahedron sharing a Mn5 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 χMT 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∼ 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 1·0.7py·1.3MeCN, which displayed sweep rate- and temperature-dependent hysteresis loops.