Triggering the Sign of Magnetic Exchange Coupling in a Dinuclear Copper(II) Complex by Solvent Molecule Coordination

The magnetic properties of a dinuclear copper(II) complex of the Schiff base ligand bis(N,N′‐3‐formylsalicylidene)‐1,3‐diaminopropan‐2‐ol (H3L) with an exogenous acetate bridging group, [Cu2L(CH3COO)] (2), and the product of its crystallization from dimethyl sulfoxide (DMSO) solution, [Cu2L(CH3COO)(DMSO)] (3), are studied experimentally and theoretically. The coordination of a DMSO molecule triggers exchange coupling from antiferromagnetic in 2 (2J = –94.8 cm–1) to ferromagnetic in 3 (2J = +121 cm–1). A combination of experimental data [XRD, X‐ray absorption spectroscopy (XAS)] and the results of DFT calculations with a broken‐symmetry approach show that the different magnetic behaviour of 2 and 3 is explained by a different conformation of the dinuclear unit, which is “symmetric” in 2 and roof‐shaped in 3. The role of the DMSO molecule in exchange‐coupling sign inversion is limited to the stabilisation of the roof‐shaped conformation of the complex. We report the first example of triggering of the sign of magnetic coupling in a dinuclear copper(II) complex by dimethyl sulfoxide (DMSO) solvation.