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.