Hydrothermal syntheses of a series of cluster-based micro-porous luminescent cadmium(ii) metal–organic frameworks with 4-amino-benzene-1,2,4-triazole: topological diversity, gas absorption and photo-luminescent characterization

Abstract

In this work the multi-dentate 4-amino-benzene-1,2,4-triazole (L1) ligand is used. A series of novel cluster-based micro-porous luminescent cadmium(II) frameworks, namely [Cd3(μ3-L1)2(μ2-L1)2(μ2-Cl)2Cl4]n (1), {[Cd2(μ3-L1)2(μ2-Br)2Br2]·1.05H2O}n (2) and {[Cd2(μ2-L1)3(L1)2(μ2-I)2]·(CdI4)·1.5H2O}n (3) have been isolated under hydrothermal conditions. 1 presents a 4-connected (4,4) topology using trinuclear Cd(II) clusters as basic nodes. For 1, two bridging μ2-Cl− anions and two bridging μ3-L1 ligands connect three neighboring CdII ions forming trinuclear Cd3 clusters. Each Cd3 cluster links four neighboring Cd3 clusters forming a 2D (two-dimensional) neutral micro-porous framework. 1D rhombic channels with dimensions of 7.594(2) A × 21.250(6) A can be observed along the c-axis. 2 presents a rare I1O3 hybrid type micro-porous framework. In 2 these bridging μ3-L1 ligands link central CdII ions forming a 3D Cd–L1 organic connectivity. Two kinds of 1D Cd–Br–Cd inorganic connectivities further consolidate the 3D Cd–L1 organic connectivity, which ultimately forms a rare I1O3 type hybrid framework. 3 presents a novel 3D cluster-based micro-porous cation framework containing 1D channels, in which guest CdI42− anions and water molecules are located. Topological analysis indicates that 3 presents a novel 4-connected dmp topology using binuclear Cd2I2 clusters as basic nodes. PXRD, TGA and Gas absorption experiments for 1–3 have also been carried out. Solid state photo-luminescent spectra of 1–3 have been determined indicating strong emission bands. For 1 selective photo-luminescent quenching for NO2− anions can be observed. The result also reveals that L1 can adopt various different coordinated modes and flexible spatial distortion dihedral angles (between aromatic benzene and triazole rings), which has great potential in the construction of these novel cluster-based micro-porous coordination frameworks.