Synthesis, structures, luminescence and magnetism of nine lanthanide complexes with three-dimensional frameworks constructed from 2-(pyridyl-N-oxide)methylphosphonic acid and oxalic acid

Abstract

To investigate the coordination nature of the pyridyl-N-oxide phosphonate ligands with rare earth metals, two series of nine lanthanide complexes, namely, {[Ln(HL)((C₂O₄)_0.5)₂(H₂O)]·3H₂O}_n {Ln = Eu(1), Gd(2), Tb(3), Dy(4) and Ho(5)} and {[Ln₂(L)(C₂O₄)₂(H₂O)₃]·H₂O}_n {Ln = Er(6), Tm(7), Yb(8) and Lu(9)} {H₂L = 2-(pyridyl-N-oxide)methylphosphonic acid; H₂C₂O₄ = oxalic acid }, have been hydrothermally synthesized and characterized by IR spectroscopy, thermogravimetric analysis, and powder and single-crystal X-ray diffraction. Complexes 1–5 are isomorphic, featuring a three-dimensional (3D) porous structure with a dia topological framework, while the isomorphic complexes 6–9 show a 3D 3,4-connected topological framework with a point symbol of {7²·8}₂{7³·8³}. Photoluminescence spectra of complexes 1 and 3 exhibit the strong luminescence characteristic of Eu(III) and Tb(III) ions, respectively, suggesting that HL⁻ and L²⁻ anions are able to efficiently sensitize the luminescence of lanthanide ions. The magnetic analyses of complexes 2–5 show the characteristic magnetic susceptibilities of isolated Gd(III), Tb(III), Dy(III) and Ho(III) ions, respectively.