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

Abstract

Seven new luminescent metal–organic frameworks (LMOFs), [Cd_1.5(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.