Porous Metal–Organic Frameworks with Multiple Cages Based on Tetrazolate Ligands: Synthesis, Structures, Photoluminescence, and Gas Adsorption Properties

Three tetrazolate-based coordination polymers [Mn­(TzA)­(H₂O)₂]_n (1, H₂TzA = 1H-tetrazole-5-acetic acid), {[Cd₅(MTz)₉]·OH}_n (2, MTz = 5-methyltetrazolate), and [Cd₃(MTz)₃Cl₃]_n (3) were synthesized via the reactions of a tetrazole ligand H₂TzA with metal ions under hydrothermal conditions. During the formation of 2 and 3, Cd­(II) ions were coordinated by MTz^–, which was generated as the result of the in situ decarboxylation of the H₂TzA ligand. Single-crystal X-ray diffraction analyses revealed that 1 possessed an infinite 2D layer structure with a μ₃-TzA^2– moiety, forming a 4⁴-sql topology, and the 2D sheets were further hydrogen-bonded to form a 3D framework. Compound 2 had a 3D porous framework with a 4⁹_·6⁶-acs topology. Compound 3 adopted a 3D porous framework with a body-centered cubic (bcu) topology, which was comprised of 48-membered (Cd₂₄Cl₂₄) rings, and it demonstrated a moderate adsorption of H₂ over N₂ as a result of its limited window size. The solid-state luminescent properties of complexes 2 and 3 and the corresponding HMTz molecule were also investigated.