Novel Lanthanide(III) Oxalatophosphonates with New Topology: Syntheses, Crystal Structures, Reversible Dehydration/Hydration, and Luminescence Properties

Hydrothermal reactions of lanthanide­(III) chlorides and H₂O₃PCH₂NCH₂(CH₂CH₂OPO₂H) (H₃L) with oxalate anion lead to six novel lanthanide oxalatophosphonates with a three-dimensional (3D) framework structure, namely, {[Ln­(H₂L)­(C₂O₄)­(H₂O)]·nH₂O}_∞ [n = 3 (compounds 1–3), 2 (compounds 4–6); Ln = Ce (1), Pr (2), Nd (3), Sm (4), Eu (5), and Tb­(6)]. Compounds 1–6 are isostructural and feature a complex 3D network built from 1D chains of lanthanide oxalate and {Ln­(H₂L)}²⁺ chains. These lanthanide oxalatophosphonates possess two types of channels with dimensions of 11.6 Å × 4.4 Å and 13.8 Å × 8.9 Å along the a- and b-axis, respectively, and these channels incorporate some crystalline water molecules therein by hydrogen-bonding interactions. They show an unusual noninterpenetrated (3,5)-connected topology. The title compounds were characterized by X-ray single-crystal diffraction and X-ray powder diffraction (XRD) as well as with infrared spectroscopy and elemental and thermogravimetric analysis. Furthermore, the temperature-dependent powder XRD, the variable temperature IR spectroscopy, and the dehydration/hydration properties of compound 2 have also been studied. Luminescent measurements indicate that the Sm (4) and Eu (5) compounds exhibit strong luminescence in yellow light and red light regions, respectively.