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.