Slow Magnetic Relaxation and Luminescence in Mononuclear Ln Complexes with Pseudo-mono-axial Ligand Field: Modulation of Magnetic Properties through Variation of an Equatorial Donor Atom

Two pairs of isostructural mononuclear Ln (III) complexes sharing the same competent ligand tris2-{ (imidazol-4-yl) methylideneaminoethyl}amine (H3L) and the alternative auxiliary ligands 8-hydroxyquinoline (H8-HQ) and salicylaldehyde (Hsal) were synthesized, namely, Ln (H3L) (8-HQ) BPh42 (Ln = Dy), 1; Eu, 3 and Ln (H3L) (sal) BPh42 (Ln = Dy, 2; Eu, 4). In all four complexes, the Ln (III) ions are nine-coordinated and exhibit an spherical-capped square antiprismatic coordination polyhedron. It is noteworthy that the neutral N-containing ligand H3L combining with the negatively charged 8-HQ–/sal– ligand affords a pseudo-mono-axial ligand field in all complexes. The Dy (III) derivatives 1 and 2 were found to exhibit slow magnetic relaxation behavior with Ueff of 82 (2) and 38. 3 (5) K, respectively. Ab initio calculations suggest that the distinctly different magnetic properties between 1 and 2 can be attributed to the change of one of the equatorial donor atoms from N to O. The luminescence properties of Eu (III) -based complexes 3 and 4 were investigated; these complexes show a brilliant emission of characteristic red light.