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

[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 ErIII 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 Ea =
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 ErIII 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 ErIII-based complexes.