Seven luminescent metal–organic frameworks constructed from 5-(triazol-1-yl)nicotinic acid: luminescent sensors for CrVI and MnO4− ions in an aqueous medium

Seven new luminescent metal–organic frameworks (LMOFs), [Cd1.5(L)2(H2O)(NO3)]n (1), [Cd(L)2(H2O)2]n (2), [Pb(L)(H2O)2(NO3)]n (3), [Pb(L)2(H2O)]n (4), [Zn(L)2(H2O)4]n (5), [Zn2(L)(btc)(H2O)2]n (6) and {[Zn(L)(p-bdc)0.5(H2O)](p-H2bdc)0.5}n (7), were assembled employing 5-(triazol-1-yl)nicotinic acid (HL) with Cd(II), Pb(II) and Zn(II) ions, revealing versatile frameworks as well as various types of coordination modes of HL. Single-crystal X-ray diffraction analyses reveal the different dimensionalities (0D, 1D, 2D or 3D) of complexes 1–7. Complex 1 displays a 3D dense-packing structure with a 3-nodal 3,4,6-connected net with a symbol of {4·64·8}2{4·2·64·89}{62·8}2. Complex 2 presents a 2D layered structure with a uninodal 4-connected sql net with a symbol of (44·62). Complex 3 shows a 1D chain based on [Pb2(COO)2(H2O)4(NO3)2N2] secondary building units (SBUs) and 4 exhibits a 1D dimeric chain. Complex 5 is a 0D structure. Complexes 6 and 7 display 2D layered structures based on binuclear [Zn2(COO)4(H2O)2N2] SBUs, which are designated as a 4-nodal 3,3,3,6-connected net with a symbol of {4·62}2{42·610·83}{63}4 and a 4-connected sql net, respectively. Further, the solid-state luminescence properties of the complexes were measured at room temperature. Meanwhile, 2 shows high selectivity and sensitivity for CrO42−, Cr2O72− and MnO4− ions by luminescence quenching effect with low detection limits, and the mechanisms of the quenching effect are discussed in detail.