Slow Magnetic Relaxation in Intermediate Spin S = 3/2 Mononuclear Fe(III) Complexes.

Magneto-structural correlation studies of mononuclear intermediate S = 3/2 Fe(III) complexes, (PMe3)2FeCl3 (1) and (PMe2Ph)2FeCl3 (2), demonstrate the influence of local symmetry on magnetic anisotropy. Symmetric compound 1 is characterized by a zero-field splitting (ZFS) parameter of D = -50(2) cm-1, leading to the observation of slow magnetic relaxation with an energy barrier of 81 cm-1 along with magnetic hysteresis up to 4 K, whereas symmetrically perturbed compound 2 displays a much reduced ZFS parameter of D = -17(1) cm-1 and energy barrier of Ueff = 46 cm-1.