Effect of auxiliary-ligand on assembly of lanthanide(III) complexes with quinoline-2-carboxylic acid: Synthesis, structure, photoluminescent and magnetic properties

A series of lanthanide complexes [Ln2(QUIN)6(H2O)6]·3H2O (Ln = Pr (1), Nd (2), Sm (3), Eu (4)), [Pr(QUIN)3(H2O)]n (5) and [Pr2(QUIN)4(phen)2(NO3)2(H2O)2] (6) were synthesized by hydrothermal reactions of corresponding lanthanide nitrates with quinoline-2-carboxylic acid (HQUIN) under intervention of auxiliary ligands, and characterized by elemental analysis, IR, TGA and single-crystal X-ray diffraction. Complexes 1–4 and 6 exhibit the dinuclear lanthanide architectures in which each Ln(III) ion is nine-coordinated and possesses distorted tricapped trigonal prism geometry. The dinuclear structures in 1–4 are further linked by the hydrogen bond interactions resulting in the formation of the two-dimensional supramolecular network, while the dinuclear structures in 6 form the three-dimensional supramolecular network. Complex 5 is composed of one-dimensional chain framework, which further pack into the two-dimensional layer through weak π⋯π stacking interactions. The supramolecular architectures 1–6 show that the numerous hydrogen bonds are responsible for the increasing thermal stability. Photoluminescence investigation reveals that complexes 4 and 6 display strong red and green emission, respectively. Moreover, the magnetic properties of 2 and 6 have also been investigated.