The Highly Connected MOFs Constructed from Nonanuclear and Trinuclear Lanthanide-Carboxylate Clusters: Selective Gas Adsorption and Luminescent pH Sensing.

The highly odd-numbered 15-connected nonanuclear [Ln9(μ3-O)2(μ3-OH)12(O2C-)12(HCO2)3] and 9-connected trinuclear [Ln3(μ3-O)(O2C-)6(HCO2)3] lanthanide-carboxylate clusters with triangular and linear carboxylate bridging ligands were synergistically combined into Ln-MOFs, [(CH3)2NH2]3{[Ln9(μ3-O)2(μ3-OH)12(H2O)6][Ln3(μ3-O)(H2O)3](HCO2)3(BTB)6}·(solvent)x (abbreviated as JXNU-3, Ln = Gd, Tb, Er; BTB3- = benzene-1,3,5-tris(4-benzoate)), displaying a (3,9,15)-connected topological net. The JXNU-3(Tb) exhibits highly selective CO2 adsorption capacity over CH4 that resulted from the high localized charge density induced by the presence of the nonanuclear and trinuclear cluster units. In addition, JXNU-3(Tb) with high chemical stability and characteristic bright green color exhibits fluorescent pH sensing, which is pertinent to the different protonation levels of the carboxylate groups of the benzene-1,3,5-tris(4-benzoate) ligand with varying pH.