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

In this work the multi-dentate 4-amino-benzene-1,2,4-triazole (L-1) ligand is used. A series of novel cluster-based micro-porous luminescent cadmium(II) frameworks, namely [Cd-3(mu(3)-L-1)(2)(mu(2)-L-1)(2)(mu(2)-Cl)(2)Cl-4](n) (1), {[Cd-2(mu 3-L-1)(2)(mu(2)-Br)(2)Br-2]center dot 1.05H(2)O}(n) (2) and {[Cd-2(mu(2)-L-1)(3)(L-1)(2)(mu(2)-l)(2)]center dot(Cdl(4))center dot 1.5H(2)O}(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 mu(2)-Cl anions and two bridging mu(3)-L-1 ligands connect three neighboring Cd-II ions forming trinuclear Cd-3 clusters. Each Cd-3 cluster links four neighboring Cd-3 clusters forming a 2D (two-dimensional) neutral micro-porous framework. 1D rhombic channels with dimensions of 7.594(2) angstrom x 21.250(6) angstrom can be observed along the c-axis. 2 presents a rare (IO3)-O-1 hybrid type micro-porous framework. In 2 these bridging mu(3)-L-1 ligands link central Cd-II ions forming a 3D Cd-L-1 organic connectivity. Two kinds of 1D Cd-Br-Cd inorganic connectivities further consolidate the 3D Cd-L-1 organic connectivity, which ultimately forms a rare (IO3)-O-1 type hybrid framework. 3 presents a novel 3D cluster-based micro-porous cation framework containing 1D channels, in which guest Cdl(4)(2-) anions and water molecules are located. Topological analysis indicates that 3 presents a novel 4-connected dmp topology using binuclear Cd(2)l(2) 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 L-1 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.