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 Zn-II/Cd-II 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 Zn-II or Cd-II salt yielded the ligand 3-(5H-tetrazolyl)benzoate (3-tzba(2-)) [3-H(2)tzba = 3-(5H-tetrazolyl)benzoic acid]. The obtained polymers are formulated as [Zn-2(3-tzba)(N-3)(OH)(2,2'-bipy)] (1), [Zn(3-tzba)(2,2'-bipy)(H2O)]center dot 3H(2)O (2), [Zn-2(3-tzba)(2)(Phen)(2)]center dot H2O (3) and [Cd-4(3-tzba)(2)(N-3)(4)(2,2'-bipy)(3)]center dot H2O (4) A crystalline mixture of Zn-II 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 Cd-II instead of Zn-II resulted in the formation of 4, which has a 2D corrugated layer structure. The 3-tzba(2-) ligands display four different coordination modes in 1-4, and modes mu(2)-kappa N2:kappa O1, O2(in 2) and mu(3)-kappa N3:kappa O1:kappa O2 (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.