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.

由具有三角和线性羧酸桥连配体的奇数15连接的非核[Ln9(μ3-O)2(μ3-OH)12(O2C−)12(HCO2)3]和9连接的三核[Ln3(μ3-O)(O2C−)6(HCO2)3]镧系羧酸盐簇协同组装而成的Ln-MOFs，[(CH3)2NH2]3{[Ln9(μ3-O)2(μ3-OH)12(H2O)6][Ln3(μ3-O)(H2O)3](HCO2)3(BTB)6}·(溶剂)x（简称为JXNU-3，Ln = Gd, Tb, Er；BTB3– = 苯-1,3,5-三(4-苯甲酸)），展现出(3,9,15)连接的拓扑网络结构。JXNU-3(Tb)在甲烷上表现出高度选择的CO2吸附能力，这归因于非核和三核簇单元的存在所诱导的高局部电荷密度。此外，具有高化学稳定性和特征明亮绿色的JXNU-3(Tb)表现出荧光pH传感特性，这与苯-1,3,5-三(4-苯甲酸)配体的羧酸基团在不同pH值下的质子化水平密切相关。