Slow magnetic relaxation in octahedral low-spin Ni(iii) complexes

Abstract

Herein we report the first examples of single-molecule magnet (SMM) behaviour in S = 1/2 Ni(III) complexes. We find that low-spin 3d⁷trans-[Ni^III(cyclam)(X)₂]Y complexes (cyclam = 1,4,8,11-tetraazacyclotetradecane; X and Y are singly charged anions) exhibit field-induced slow relaxation of magnetization for O-donor axial ligands (nitrate) but not for N-donor variants (isothiocyanate). Experimental and electronic structure computational investigations indicate that intrinsic spin polarisation of low-spin Ni(III) is modulated significantly by local coordination geometry and supramolecular interactions. Solid state dilution of Ni(III) with diamagnetic Co(III) ions forms a related complex salt, [Ni_xCo_1−x(cyclam)(NO₃)₂](NO₃)·2HNO₃ (0.1 < x < 1), which preserves slow magnetic dynamics, thus supporting a molecular component to slow relaxation. An initial analysis of magnetic relaxation lifetime fits best to a combination of Raman and direct relaxation processes.