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, [Cu2(L1)2(N3)2]·DMF (1), [Cu2(L2)2(N3)2] (2),
[Cu2(L3)2(NCS)2] (3), and [Cu2(L4)2(N3)2] (4) {where HL1, HL2, HL3, and HL4 are tridentate
N2O donor Schiff bases}, are synthesized and characterized.
Complexes 1, 2, and 3 possess
π···π 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 π···π stacking interactions, while
ferroelectric ordering is observed in complexes 1 and 3 due to hydrogen-bonding interactions. Most interestingly,
complex 1, which contains both π···π
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.