Studies of magnetic properties and HFEPR of octanuclear manganese single-molecule magnets

Abstract

A new octanuclear manganese cluster [Mn₈(Hpmide)₄O₄(EtCOO)₆](ClO₄)₂ (1) is achieved by employing Hpmide as the ligand, and this paper examines the synthesis, X-ray structure, high-field electron paramagnetic resonance (HFEPR), magnetization hysteresis loops and magnetic susceptibilities. Complex 1 was prepared by two different methods, and hence, was crystallized in two space groups: P3₂21 for 1a and P3₁21 for 1b. Each molecule possesses four Mn^II and four Mn^III ions. The metal-oxo framework of complex 1 consists of three face-sharing cubes with manganese ions on alternate corners. The four Mn^III cations have their Jahn–Teller elongation axes roughly parallel to the c axis of the crystal lattice. The dc magnetic susceptibility measurements reveal a spin-frustration effect in this compound. The ac magnetic susceptibilities, as well as the magnetization hysteresis measurements, clearly establish that complex 1a is a single-molecule-magnet (SMM) with a kinetic energy barrier (10.4 cm⁻¹) for spin reversal. HFEPR further confirms that complex 1a is a new SMM with a magnetoanisotropy and quantized energy levels. However, interpretation of the complete set of measurements in terms of a well defined spin ground state is not possible due to the spin frustration.