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

Abstract

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 χ_MT 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.