Novel Luminescent Lanthanide(III) Diphosphonates with Rarely Observed Topology

Hydrothermal reactions of lanthanide(III) salts with N-(2-pyridyl)-aminomethane-1,1-diphosphonic acid (H4L) led
to five new lanthanide(III) phosphonates, namely, La4(H2L)4(H3L)4(H2O)4·20H2O (1) and Ln(H2L)(H3L)·4H2O (Ln = Eu (2), Gd
(3), Dy (4), and Er (5)). Compound 1 features a 3D framework with rarely observed topology in which each lanthanum(III) ion is
eight-coordinated by seven phosphonic oxygen atoms from four phosphonate ligands and an aqua ligand. It possesses two types of
tunnels running parallel to the a-axis, one formed by five La(III) ions and five organic moieties, the other by seven La(III) ions and
seven organic moieties. It shows noninterpenetrated three-connected topology. Compounds 2−5 are isostructural and exhibit one-dimensional chain structures in which each pair of Ln(III) ions are bridged by two and four phosphonate groups, alternatively.
Compound 2 exhibits emission bands of the phosphonate ligand and the europium(III) ion in the visible region under 360 nm
excitation, with a Eu (5D0) lifetime of 1.2 ms. Compound 3 displays a very broad ligand-centered emission band (λmax = 412 nm)
in the blue light region. Compound 5 is a luminescent material in the near-IR region.