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

Herein we report the first examples of single-molecule magnet (SMM) behaviour in S = 1/2 Ni(iii) complexes. We find that low-spin 3d(7)trans-[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(x)Co(1–x)(cyclam)(NO(3))(2)](NO(3))·2HNO(3) (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.