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, La-4(H2L)(4)(H3L)(4)(H2O)(4)center dot 20H(2)O (1) and Ln(H2L)(H3L)center dot 4H(2)O (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 (D-5(0)) lifetime of 1.2 ms. Compound 3 displays a very broad ligand-centered emission band (lambda(max) = 412 nm) in the blue light region. Compound 5 is a luminescent material in the near-IR region.