Half-Integer Spin Heptanuclear Single-Molecule Magnet with an Unusual MnIII6MnII Exchange-Coupled Core

The synthesis, X-ray crystallography, magnetic properties, and high-field electron paramagnetic resonance (HFEPR) of a new heptanuclear manganese complex [Mn7(heamp)6]­(ClO4)2·4CH2Cl2·H2O (complex 2), in which heampH3 is 2-[N,N-di­(2-hydroxyethyl)­aminomethyl]­phenol (compound 1), is reported. Complex 2 has a hexagonal, disk-shaped topology and contains six Mn­(III) ions and a central Mn­(II) ion. It crystallizes in the monoclinic space group P21/c with two molecular orientations. Consideration of the cluster topology, together with variable-temperature and variable-field DC magnetic susceptibility data, suggest that complex 2 exists in a half-integer, S = 19/2 ± 1 spin ground state, with appreciable uniaxial zero-field splitting (D = −0.16 cm–1). AC magnetic susceptibility measurements clearly show out-of-phase signals, which are frequency- and temperature-dependent, indicating slow magnetization relaxation behavior. An analysis of the relaxation data employing the Arrhenius formula yielded an effective relaxation barrier of 12.9 cm–1. Simulations of HFEPR studies agree with the assignment of an S ≈ 19/2 spin ground state, with g = 1.96, D = −4.71 GHz (−0.16 cm–1), and a longitudinal fourth-order zero-field splitting parameter B40 = −2.7 × 10–4 GHz (−9.0 × 10–6 cm–1).