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 Cd^II 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) Å × 21.250(6) Å 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 Cd^II 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.