Luminescent Zinc(II) Coordination Polymers of Bis(pyridin-4-yl)benzothiadiazole and Aromatic Polycarboxylates for Highly Selective Detection of Fe(III) and High-Valent Oxyanions

The hydro(solvo)thermal reactions of Zn(NO3)2·6H2O, bis(pyridin-4-yl)benzothiadiazole (BTD-bpy), and benzene-1,3,5-tricarboxylic acid (H3btc) or naphthalene-1,4-dicarboxylic acid (1,4-H2ndc) yielded the corresponding coordination polymers {[Zn2(Hbtc)2(BTD-bpy)(MeOH)2]·MeOH}n (1) and {[Zn2(1,4-ndc)2(BTD-bpy)]·0.5MeOH·H2O}n (2), respectively. Compound 1 has a two-dimensional (2D) decorated layer structure of an sql net with sufficient free volumes of 19.8%. Compound 2 exhibits a three-dimensional (3D) pillared-layer open framework of a pcu net; two such identical frameworks are mutually interpenetrated with each other to form overall 2-fold interpenetating frameworks with sufficient free volumes of 19.8%. Compounds 1 and 2 both showed blue fluorescence in the solid state and in different solvent suspensions. The luminescence properties of 1 and 2 were exploited as multiresponsive luminescence sensors for the sensitive detection of Cr2O72– and MnO4– with a low detection limit and high selectivity over other anions in DMF suspensions through luminescence quenching. Additionally, the same DMF suspensions were also utilized to selectively recognize trace amounts of Fe3+ among large pools of different metal ions with excellent anti-interference ability, high sensitivity, and low detection limit. Of particular note, compounds 1 and 2 exhibited two different modes for Fe3+ detection, showing an abnormous luminescence enhancement–quenching (turn-on–turn-off) sensing mechanism for the former and a regular luminescence quenching (turn-off) response for the latter.