Field-Induced Ferromagnetism and Multiferroic Behavior in End-on Pseudohalide-Bridged Dinuclear Copper(II) Complexes with Tridentate Schiff Base Blocking Ligands

Four new end-on pseudohalide-bridged dinuclear copper(II) complexes, (Cu-2(L-1)(2)(N-3)(2)]center dot DMF (1), (Cu-2(L-2)(2)(N-3)(2)] (2), [Cu-2(L-3)(2)(NCS)(2)] (3), and [Cu-2(L-4)(2)(N-3)(2) (4) {where HL1, HL2, HL3, and HL4 are tridentate N2O donor Schiff bases), are synthesized and characterized. Complexes 1, 2, and 3 possess pi center dot center dot center dot pi stacking interactions, while in addition hydrogen-bonding interactions are present in 1 and 3. However, by contrast, complex 4 contains neither type of interaction. Field-induced long-range ferromagnetic ordering beyond 0.9 T is observed in complexes 1 and 2 due to pi center dot center dot center dot pi stacking interactions, while ferroelectric ordering is observed in complexes 1 and 3 due to hydrogen-bonding interactions. Most interestingly, complex 1, which contains both pi center dot center dot center dot pi stacking and hydrogen-bonding interactions, shows multiferroic behavior as a result of coupling between the dielectric and magnetic fields with 8% change in the magneto-dielectric-effect at room temperature. We believe that from this study will emerge a new class of multiferroic materials.