Design and Synthesis of Four Newly Water-Stable Pb-Based Heterometallic Organic Frameworks: How Do the Second Metals (Zn, Cd, Co, and Mn) Optimize Their Fluorescent and Catalytic Properties?

In this work, a new stable monometallic Pb-based metal–organic framework (MOF) [PbL] n ( 1 ) was obtained by a designed N,O-containing ligand 5-(1 H -tetrazol-5-yl)isophthalic acid (H 2 L) for the first time. On the basis of the hard and soft acids and bases (HSAB) principle and the multicoordination modes of L 2– and Pb(II) ions, four new heterometallic MOFs (HMOFs), namely, {[PbM 0.5 L(H 2 O) 2 ]·2H 2 O} n (M = Zn ( 2 ), Cd ( 3 ), Co ( 4 ), and Mn ( 5 )), have been further synthesized by introducing the second metals into the synthesis process of 1, respectively. Complex 1 shows a 3D compact packing structure, while HMOFs 2 – 5 show the homogeneous 3D porous reticular structures embedding 1D channels with multiple active sites (the unsaturated metal sites and uncoordinated N sites) viewed along the b direction. The resultant HMOFs possess high hydrolytic and thermal stability, owing to the abundant π···π interactions for the neighboring phenyl rings in the L 2– ligands. Of great importance, it is found that the enhanced luminescence intensities of HMOFs 2 and 3 and the catalytic performances of HMOFs 4 and 5 are demonstrated in comparison with 1 . HMOFs 2 and 3 are successfully explored as the nitrobenzene sensors with lower detection limits, and HMOFs 4 and 5 are the outstanding catalysts for the CO 2 cycloaddition. This work may provide some valuable references for the performance variations of one specific monometallic MOF to HMOF materials by introducing the closed/open-shell electron configuration of the second metal ions.