Crystal Structures and Magnetic and Luminescent Properties of a Series of Homodinuclear Lanthanide Complexes with 4-Cyanobenzoic Ligand

A series of homodinuclear lanthanide(III) complexes with the 4-cba ligand, [La2(4-cba)6(phen)2(H2O)6] (1) and
[Ln2(4-cba)6(phen)2(H2O)2] (Ln = Pr (2), Nd (3), Sm (4), Eu (5), Gd (6), and Dy (7); 4-Hcba = 4-cyanobenzoic
acid; phen = 1,10-phenanthroline), have been synthesized and structurally characterized by single-crystal X-ray
diffraction. In 1, two water molecules bridge two nine-coordinated La ions, and six 4-cba ligands coordinate to the
two La ions in terminal mode. In the isostructural complexes 2−7, two eight-coordinated Ln ions are connected by
four bidentate 4-cba ligands, and another two 4-cba ligands terminate the two Ln ions. The variable-temperature
magnetic properties of 2−7 have been investigated. Complex 7 shows a significant ferromagnetic interaction between
Dy(III), while no magnetic interaction exists between Gd(III) ions in 6. In 2−5, the value of χMT decreases with
decreasing temperature, but the magnetic interactions between the Ln(III) ions cannot definitely be concluded.
Notably, the spin−orbit coupling parameters, λ, for Sm(III) (216(2) cm-1) and Eu(III) (404(2) cm-1) have been
obtained in 4 and 5, respectively. The strong fluorescent emissions of 4, 5, and 7 demonstrate that ligand-to-Ln(III)
energy transfer is efficient and that the coordinated water molecules do not quench their luminescence by the
nonradiative dissipation of energy.