Syntheses, structures, luminescence and CO2 gas adsorption properties of four three-dimensional heterobimetallic metal–organic frameworks

A new pyridyl-tricarboxylic acid ligand, 4,4'-(6-carboxypyridine-2,4-diyl)dibenzoic acid (H3L), was used to construct one zero-dimensional (0D) complex, [Co(H2L)2(H2O)2]•2H2O (1), and four isostructural three-dimensional (3D) heterobimetallic metal-organic frameworks (MOFs), [MNa(L)(H2O)]n•solvents (M ​= ​Co (2), Ni (3), Cu (4) and Zn (5)). The dimensionality ranging from 0D complex (1) to 3D frameworks (2–5) should be ascribed to various solvents (from MeCN to DMA/DMF) or whether presence of Na+ cation or not. Interestingly, isostructural 3D heterobimetallic MOFs 2–5 possess rhombic voids and reveal CO2 gas adsorption features. Because heterobimetallic MOFs 2 and 5 possess higher framework stability than 3 and 4, 2 and 5 exhibit higher CO2 adsorption capacities at 273 ​K. Furthermore, photoluminescence properties of 1–5 have also been investigated. The present work provides a promising approach to design and construct heterobimetallic MOFs containing alkali-metal cations, and then to tune CO2 adsorption properties.