Lanthanide-organic frameworks constructed from naphthalenedisulfonates: structure, luminescence and luminescence sensing properties

Two series of Ln(3+)-coordination frameworks were synthesized by using positional isomers of naphthalenedisulfonate (Nds) ligands, along with oxalate (ox) and 1,10-phenanthroline (phen) ligands under the same experimental conditions, namely, {[Ln(1,5-Nds)(0.5)(ox)(phen)(H2O)]center dot H2O}(n) (Ln = Eu (1), La (2), and Sm (3)), [La(2,6-Nds)(ox)(0.5)(phen)(2)(H2O)](n) (4) and [Ln(2,6-Nds)(0.5)(ox)(phen)(H2O)](n) (Ln = Eu (5), Gd (6), and Tb (7)). Compounds 4 and 5-7 show different grid-like layers with a {6(3)} topology based on [LaO5N4] and [LnO(6)N(2)] polyhedra as uninodal nodes, respectively. However, the 1,5-Nds-based linker can pillar into a high dimensionality pillared-layer microporous motif of complexes 1-3 with a {3(6.)4(8.)5(6.)6} topology based on {LnO(7)N(2)} polyhedra as uninodal nodes, affording one-dimensional channels. Notably, highly luminescent microporous pillared-layer Eu3+-framework 1 is a promising luminescence sensor for small organic molecules and metal ions, especially for benzaldehyde and Fe3+. The luminescence behavior of 1 is affected by the solvents and the luminescence color changes from red-pink to blue. The possible luminescence sensing mechanism for Fe3+ and the effect of using different solvents on the luminescence sensing of metal ions were explored. It is noteworthy that complex 1 can be excited with a longer excitation wavelength (358 nm), which is an important requirement for applications.