Multiple magnetic relaxation pathways in T-shaped N-heterocyclic carbene-supported Fe(i) single-ion magnets

Abstract

The magnetic properties of the T-shaped three-coordinate complexes, namely, [(sIMes)₂Fe(THF)][BPh₄] (1, sIMes: 1,3-bis(2′,4′,6′-trimethylphenyl)-imidazolin-2-ylidene) and [(cyIMes)₂Fe(THF)][BPh₄] (2, cyIMes: 1,3-bis(2′,4′,6′-diethylphenyl)-4,5-(CH₂)₄-imidazol-2-ylidene) and quasi-linear two-coordinate complexes [(sIDep)₂Fe][BAr^F₄] (3, sIDep: 1,3-bis(2′,6′-diethylphenyl)-imidazolin-2-ylidene; Ar^F: 3,5-di(trifluoromethyl)phenyl) and [(cyIDep)₂Fe][BAr^F₄] (4, cyIDep: 1,3-bis(2′,6′-diethylphenyl)-4,5-(CH₂)₄-imidazol-2-ylidene) were studied. Magnetic characterization indicated the unquenched first-order angular momentum and large zero-field splitting. AC susceptibility measurements showed that the T-shaped three-coordinate Fe(I) complexes exhibited field-induced relaxation of magnetization. The Direct, resonant quantum tunneling, and Raman processes were observed and contributed to the determination of the overall magnetic relaxations.