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

Abstract

Two series of Ln³⁺-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)]·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 {6³} topology based on [LaO₅N₄] and [LnO₆N₂] 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 {3⁶·4⁸·5⁶·6} topology based on {LnO₇N₂} 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.