Modulating Single-Molecule Magnetic Behavior of a Dinuclear Erbium(III) Complex by Solvent Exchange

Abstract

[Er₂(thd)₄Pc]·2C₆H₆ (1) (Hthd = 2,2,6,6-tetramethylheptanedione), obtained as green crystals from the reaction of [Er(thd)₃]·2H₂O with lithium phthalocyanine, Li₂Pc, is a stable dinuclear complex with two Er^III centers. Its lattice benzene solvent can be exchanged by soaking the crystals in dichloromethane to give [Er₂(thd)₄Pc]·2CH₂Cl₂ (2). The magnetic susceptibility data suggest different coupling interactions for the two complexes. While 1 exhibits fast relaxation and an estimated energy barrier of E_a = 2.6 cm^-1 under 600 Oe dc field, the single-molecule magnet behavior of 2 is field-induced and the energy barrier is higher at 34.3 cm^-1. Ab initio calculations were performed to understand the nature of the coupling interaction between two Er^III ions bridged by the phthalocyanine and the origin of different magnetic behavior. Importantly, the single-molecule magnetic properties can be reversibly tuned through the exchange of solvent molecules, confirmed by further measurements on the reverse solvated complexes 1-re and 2-re. This subtle control of relaxation by lattice solvents is rarely observed in single-molecule magnets, especially for Er^III-based complexes.