Ln(iii) complexes (Ln = Eu, Gd, Tb, Dy) with a chiral ligand containing 1,10-phenanthroline and (–)-menthol fragments: synthesis, structure, magnetic properties and photoluminescence

Abstract

A series of lanthanide(III) complexes based on the new chiral ligand L, which contains 1,10-phenanthroline and (–)-menthol fragments, namely [LnL₂(NO₃)₃] (Ln = Eu (1), Gd (2), Tb (3), Dy (4)), have been synthesized and structurally characterized. Complexes 1–4 are isostructural and crystallize in the non-centrosymmetric space group P4₁2₁2. The mononuclear complexes comprise a 10-coordinate Ln³⁺ ion with two bidentate N,N-donor ligands (L) and three bidentate chelating nitrate groups. The magnetic properties of complexes 1–4 are determined mainly by the Ln³⁺ ions. In the case of complexes 3 and 4, significant anisotropy results in nonlinear field dependences of magnetization at low temperature. Complexes 1, 3 and 4 exhibit metal-centered red (Eu³⁺), green (Tb³⁺) and yellow (Dy³⁺) luminescence, respectively, whereas complex 2 displays blue ligand-based luminescence in the solid state at room temperature. The luminescence quantum yield for the solid samples increases in the order 4 < 2 ≈ 3 < 1. The europium(III) complex shows long luminescence lifetimes (up to 1750 μs) and a very high quantum yield (φ_f = 0.87); these make this compound promising for application in sensing and optoelectronics.