Three photoluminescent zinc coordination polymers (CPs), {[Zn(tpeb)(2,5-tdc)(2,5-Htdc)]·2HO} (1), {[Zn(tpeb)(1,4-ndc)(1,4-Hndc)]·2.6HO} (2), and {[Zn(tpeb)(2,3-ndc)]·HO} (3) (tpeb = 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene, 2,5-tdc = 2,5-thiophenedicarboxylic acid, 1,4-ndc = 1,4-naphthalenedicarboxylic acid, and 2,3-ndc = 2,3-naphthalenedicarboxylic acid) were prepared from reactions of Zn(NO)·6HO with tpeb and 2,5-Htdc, 1,4-Hndc, or 2,3-Hndc under solvothermal conditions. Compound 1 has a two-dimensional (2D) grid-like network formed from bridging 1D [Zn(tpeb)] chains via 2,5-tdc dianions. 2 and 3 possess similar one-dimensional (1D) double-chain structures derived from bridging the [Zn(tpeb)] chains via pairs of 1,4-ndc or 2,3-ndc ligands. The solid-state, visible emission by 1-3 was quenched by Cr, CrO, and CrO ions in water with detection limits by the most responsive complex 3 of 0.88 ppb for Cr and 2.623 ppb for CrO (pH = 3) or 1.734 ppb for CrO (pH = 12). These values are well below the permissible limits set by the USEPA and European Union and the lowest so far reported for any bi/trifunctional CPs sensors. The mechanism of Cr luminescence quenching involves irreversible coordination to free pyridyl sites in the CP framework, while the Cr quenching involves reversible overlap of the absorption bands of the analytes with those of the excitation and/or emission bands for 3.
