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 (O2 C-)12 (HCO2 )3 ] and 9-connected trinuclear [Ln3 (μ3 -O)(O2 C-)6 (HCO2 )3 ] lanthanide-carboxylate clusters with triangular and linear carboxylate bridging ligands were synergistically combined into Ln-MOFs, [(CH3 )2 NH2 ]3 {[Ln9 (μ3 -O)2 (μ3 -OH)12 (H2 O)6 ][Ln3 (μ3 -O)(H2 O)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.