Construction of 2D zinc(ii) MOFs with tricarboxylate and N-donor mixed ligands for multiresponsive luminescence sensors and CO2 adsorption†

The solvothermal reactions of ZnCl₂·6H₂O, benzene-1,3,5-tribenzoic acid (H₃btb), and N-heterocyclic ancillary imidazole (Im) or aminopyrimidine (a mp) ligands led to the creation of two-dimensional (2D) zinc(II) based metal–organic frameworks (MOFs), (Me₂NH₂)₂[Zn₂(btb)₂(Im)₂]·2DMF·3MeOH (1) and (Me₂NH₂)₂[Zn₂(btb)₂(amp)]·H₂O·2DMF·MeOH (2). The btb³⁻ ligands in 1 and 2 form an anionic 2D layered structure with a (6³) honeycomb (hcb) topology by linking to Zn(II) centres through their carboxylate groups. The incorporation of N-heterocyclic auxiliary ligands Im and amp into the hcb nets resulted in the formation of a 2D hydrogen-bonded and covalently pillared bilayer structure featuring two-fold interpenetrating networks. Each of these networks consists of small channels that are occupied by Me₂NH₂ cations and solvent molecules. Both 1 and 2 emit blue luminescence emissions in the solid state at room temperature and exhibit a great selectivity and sensitivity for the detection of acetone and multiple heavy metal ions including Hg²⁺, Cu²⁺, Fe²⁺, Pb²⁺, Cr³⁺, and Fe³⁺ ions. At 1 bar, activated 1 and 2 demonstrate moderate capacities for adsorbing CO₂ at room temperature, with a preference for CO₂ over N₂. Notably, at higher pressures (up to 20 bar), their activated samples 1 and 2 show a temperature-dependent enhancement of CO₂ uptake while retaining good stability.