Zinc(II) and Cadmium(II) Coordination Polymers Based on 3-(5H-Tetrazolyl)benzoate Ligand with Different Coordination Modes: Hydrothermal Syntheses, Crystal Structures and Ligand-Centered Luminescence

Hydrothermal reaction of Na(3‐cba) (3‐cba = 3‐cyanobenzoate), NaN3 and a metal salt with either 2,2′‐bipyridine (2,2′‐bipy) or 1,10‐phenanthroline (phen) afforded four novel ZnII/CdII polymers, which have been structurally characterized by single‐crystal X‐ray diffraction analysis. In situ [2 + 3] cycloaddition reaction of nitrile and azide in the presence of a ZnII or CdII salt yielded the ligand 3‐(5H‐tetrazolyl)benzoate (3‐tzba2–) [3‐H2tzba = 3‐(5H‐tetrazolyl)benzoic acid]. The obtained polymers are formulated as [Zn2(3‐tzba)(N3)(OH)(2,2′‐bipy)] (1), [Zn(3‐tzba)(2,2′‐bipy)(H2O)]·3H2O (2), [Zn2(3‐tzba)2(phen)2]·H2O (3) and [Cd4(3‐tzba)2(N3)4(2,2′‐bipy)3]·H2O (4). A crystalline mixture of ZnII polymers 1 and 2 with infinite ladder‐like chain and zigzag chain structures, respectively, was obtained from the reaction in the presence of 2,2′‐bipy. The replacement of 2,2′‐bipy with phen as an auxiliary ligand yielded 3, which shows a pearl‐necklace‐like chain structure. Further, the introduction of CdII instead of ZnII resulted in the formation of 4, which has a 2D corrugated layer structure. The 3‐tzba2– ligands display four different coordination modes in 1–4, and modes μ2‐κN2:κO1,O2 (in 2) and μ3‐κN3:κO1:κO2 (in 3) are observed in tetrazolate‐5‐carboxylate polymers for the first time. Photoluminescent studies in the solid state at room and low temperature revealed that 1–4 exhibit interesting luminescent behaviors, and the relevant density of states (DOS) calculation results showed that their photoluminescence mainly originates from ligand‐centered emission and is dependent on the organic ligand incorporated into the polymer. Four ZnII/CdII coordination polymers based on the 3‐(5H‐tetrazolyl)benzoate (3‐tzba2–) ligand exhibit various polymeric frameworks with the introduction of different auxiliary ligands. The 3‐tzba2– liganddisplays flexible coordination modes. Ligand‐centered photoluminescent emissions are active in these polymers and can bealtered by changing the organic ligands in the polymer.