Isostructural lanthanide oxalatophosphonates Ln(5pm8hqH3)(C2O4)1.5(H2O)·2H2O [Ln(iii) = Eu, Gd, Tb, Dy] (5pm8hqH3 = 5-phosphonomethyl-8-hydroxyquinoline): structures, magnetic and fluorescent properties

Abstract

Isostructural lanthanide oxalatophosphonates Ln(5pm8hqH₃)(C₂O₄)_1.5(H₂O)·2H₂O [Ln(III) = Eu(1), Gd(2), Tb(3), Dy(4)] have been obtained through hydrothermal reactions of 5-phosphonomethyl-8-hydroxyquinoline (5pm8hqH₃), oxalate, and Ln(NO₃)₃·6H₂O. Four compounds reveal layer structures, in which {LnO₈} polyhedra are linked through oxalate units into a netlike {Ln(C₂O₄)_1.5}_n layer containing 24-member ring composed of six Ln(III) ions and six oxalate anions. The noncoordinated 8-hydroxyquinoline groups protrude from two sides of the layer. Neighboring layers are further connected to each other through hydrogen bonds and aromatic stacking of the 8-hydroxyquinoline rings, forming a supramolecular 3D structure. In magnetic measurements, compound 2 shows weak antiferromagnetic interactions. The magnetic behaviors of 1, 3 and 4 are ascribed to the depopulation of the Stark levels and weak antiferromagnetic interactions. In the solid-state fluorescent measurements, strong ligand-centered emissions and weak Ln(III)-centered emissions can be observed for 1 and 4, while only ligand-centered emissions for 2 and 3.