Construction of lanthanide metal–organic frameworks with highly-connected topology based on a tetrapodal linker

Abstract

By using a rigid tetrapodal linker 4,4′,4′′,4′′′-silanetetrayltetrabenzoic acid (H₄L) and lanthanide metal ions, three new coordination polymers, namely, [NdL(H₂O)][NH₂(CH₃)₂]·(DMF)_x·(H₂O)_y (x ≈ 2, y ≈ 4) (1), [Eu₄L₃(H₂O)₆]·(DMF)_y·(H₂O)_x (x ≈ 2, y ≈ 4) (2) and [Er₄L₃(H₂O)₆]·(DMF)_x·(H₂O)_z (x ≈ 2, z ≈ 5) (3), were solvothermally synthesized and structurally characterized. Compound 1 is a 3D framework with a (4,8)-connected flu structure, built from distorted cuboid dinuclear neodymium–carboxylate building block and a 4-connected tetrahedral L ligand. Compounds 2 and 3 are isostructural, possessing a non-interpenetrated three-dimensional network with rare (4,4,12) highly-connected topology. In compounds 2 and 3, the fully deprotonated L⁴⁻ ligands act as pseudotetrahedral 4-connecting nodes and S-shaped tetranuclear lanthanide metal–carboxylate building blocks act as 12-connecting nodes. Compound 1 possesses permanent porosity as confirmed by N₂, H₂, O₂, CO₂ and CH₄ gas adsorption measurements.