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-(1H-tetrazol-5-yl)isophthalic acid (H2L) for the first time. On the basis of the hard and soft acids and bases (HSAB) principle and the multicoordination modes of L2– and Pb(II) ions, four new heterometallic MOFs (HMOFs), namely, {[PbM0.5L(H2O)2]·2H2O}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 L2– 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 CO2 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.