Anion Effects on the Structural and Magnetic Properties of a Series of Trinuclear CuII-LnIII-CuII Complexes.

Two series of heterometallic CuII 2LnIII complexes, ([Cu2Ln-(H 4 L)2(MeOH)2Br]-(MeOH)4(Et2O)-(Br2), where Ln = Y (1), Gd (2), Er (3), Tb (4)), and ([Cu2Ln-(H 4 L)2(MeOH)2Cl2]-(MeOH)4(Et2O)-Cl, where Ln = Y (5), Gd (6), Er (7), Tb (8), and H6L = (N,N'-bis-(2,3,4-trihydroxybenzylidene)-1,2-phenylenediamine), were designed, synthesized, and characterized through X-ray and magnetic analyses. X-ray analysis revealed that the bromide containing complexes 1-4 possessed identical supramolecular arrangements, crystallizing in layers of 2D sheets, while chloride containing complexes 5-8 formed a 3D supramolecular lattice possessing an additional π-π stacking interaction per complex. DC magnetic susceptibility measurements showed that complexes 3 and 7 exhibited antiferromagnetic coupling between copper and erbium centers while the gadolinium (2 and 6) and terbium (4 and 8) containing complexes displayed ferromagnetic CuLn coupling upon cooling. AC magnetic susceptibility measurements revealed that complexes 4 and 8 also displayed zero-field SMM behavior with U eff = 17.8 and 16.0 K, respectively. The larger bromide anion in complex 4 aids in the isolation of the magnetic centers, resulting in a U eff value higher than that of the chloride analogue.