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.