From zero-dimensional metallomacrocycle to three-dimensional metal–organic frameworks mediated by solvent polarity: near-white light emissions and gas adsorption properties

Abstract

Under the solvothermal condition, the reaction of 4,4′′-(1,3-phenylene)-bis[2,3′-bipyridine]-6-carboxylic acid (H₂L1) with Mn(NO₃)₂·4H₂O in dimethylacetamide (DMA) afforded a novel zero-dimensional (0D) metallomacrocycle, [Mn₄(L1)₄(H₂O)₈]·20H₂O (1). However, in a similar solvothermal condition to 1, the reaction of H₂L1 with Mn(OAc)₂·4H₂O in dimethylsulfoxide (DMSO) yielded one new three-dimensional (3D) metal–organic framework, [Mn(L1)]·4H₂O·DMSO (2). Furthermore, other three 3D metal–organic frameworks, [M(L1)]·4H₂O·DMSO (M = Cd (3), Cu (4) and Zn (5)), were obtained under the same solvothermal condition as 2, which are isostructural with 2. Interestingly, a novel two-dimensional (2D) metallomacrocycle network, [Zn₂(L2)(H₂O)₃]·3H₂O·DMA (6), was solvothermally synthesized through the reaction between 4,4′-(6,6′-([1,1′-biphenyl]-4,4′-diyl)bis(2-(4-carboxyphenyl)pyridine-6,4-diyl))dibenzoic acid (H₄L2) and Zn(NO₃)₂·6H₂O in DMA. 1–6 were fully characterized by infrared spectra, elemental analyses, thermogravimetric analyses, powder X-ray diffraction patterns, or single-crystal X-ray diffractions. The changes from 0D metallomacrocycle (1) to 3D isostructural metal–organic frameworks (2–5) are mediated by increasing solvent polarity (from DMA to relatively high polar DMSO) because the more polar DMSO solvent helps the coordination sites of L1²⁻ ligand to take part in coordination. More interestingly, 3, 5, and 6 achieve close to white-light emission upon excitation at 365 nm. The gas adsorption properties of 2–5 have also been investigated, and the results indicate that the CO₂ adsorption capacities are relative to the framework stability of MOFs 2–5. The present work provides a promising approach to constructing novel metal–organic frameworks or metallomacrocycles and may open new perspectives for developing single-component white-light-emitting materials.