Solvent-induced diversity of luminescent metal–organic frameworks based on different secondary building units

Abstract

By using a symmetrical V-shaped rigid 5′-carboxyl-(1,1′-3′,1′′-terphenyl)-4,4′′-dicarboxylic acid (H₃L), three Cd(II)-based metal–organic frameworks (MOFs), [Cd₃(L)₂(H₂O)₄]·DMF (1), [Cd₂(L)(SO₄)₂]·3(Me)₂NH₂ (2) and [Cd(HL)(H₂O)]·0.5H₂O (3), have been synthesized under solvothermal conditions. Due to the reactions in different solvent systems, L³⁻/HL²⁻ in 1–3 show different coordination modes with Cd(II) ions to form various secondary building units (SBUs) in the final structures. The desolvated structure of 1 (1a) contains two shapes of 1D channels with suitable pore sizes. 2 is a 3D dense packing pattern with a three nodal (5,6,7)-connected new topological net, and 3 is a 2D layered (4,4)-connected sql network connected with partly deprotonated HL²⁻ ligands. As a result, 1a possesses not only high CO₂ loading but also excellent CO₂/CH₄ selectivity. In addition, all complexes display solid-state luminescence stemming from ligand-to-metal charge transfer.