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.