Azide-Coordination in Homometallic Dinuclear Lanthanide(III) Complexes Containing Nonequivalent Lanthanide Metal Ions: Zero-Field SMM Behavior in the Dysprosium Analogue.

A series of homometallic dinuclear lanthanide complexes containing nonequivalent lanthanide metal centers [Ln(2)(LH(2))(LH)(CH(3)OH)(N(3))]·xMeOH·yH(2)O [1, Ln = Dy(III), x = 0, y = 2; 2, Ln = Tb(III), x = 1, y = 1] have been synthesized [LH(4) = 6-((bis(2-hydroxyethyl)amino)-N’-(2-hydroxybenzylidene)picolinohydrazide] and characterized. The dinuclear assembly contains two different types of nine-coordinated lanthanide centers, because the nonequivalent binding of the azide co-ligand as well as the varying coordination of the deprotonated Schiff base ligand. Detailed magnetic studies have been performed on the complexes 1 and 2. Complex 1 and its diluted analogue (1(5%)) are zero-field SMMs with effective energy barriers (U(eff)) of magnetization reversal equal to 59(3) K and 66(3) K and relaxation times of τ(0) = 10(4) × 10(-6) s and 10(4) × 10(-8) s, respectively. On the other hand, complex 2 shows a field-induced SMM behavior. Combined ab initio and density functional theory calculations were performed to explain the experimental findings and to unravel the nature of the magnetic anisotropy, exchange-coupled spectra, and magnetic exchange interactions between the two lanthanide centers.