Chemosensing of Chloride Based on a Luminescent Platinum(II) NCN Pincer Complex in Aqueous Media
2014-02-24T00:00:00Z (GMT) by
The new luminescent platinum(II) pincer complex [Pt(NCN)(S)]TfO (<b>I</b>; NCN = 1,3-bis(2-<i>N</i>-phenylbenzimidazolyl)benzene, S = solvent, and TfO<sup>–</sup> = triflate anion) was synthesized and studied as a chemosensor for chloride in aqueous media. In 50 vol % aqueous DMF or CH<sub>3</sub>CN chloride quenches the fluorescence with association constants of 1.2 × 10<sup>3</sup> and 81 M<sup>–1</sup>, respectively. On the other hand, in the micellar medium of cetyltrimethylammonium hydrogensulfate at pH 7.0 additions of inorganic anions to <b>I</b> enhance the fluorescence with a pronounced selectivity toward chloride, which shows also much tighter binding to the receptor with association constant 7.9 × 10<sup>4</sup> M<sup>–1</sup> in comparison to that in mixed organic solvents. On basis of <sup>1</sup>H NMR titration experiments and the crystal structure of the neutral chloro complex of <b>I</b> the binding mode of chloride is proposed involving the coordination of chloride to the Pt(II) atom with simultaneous formation of intramolecular short C–H···Cl–Pt contacts. The combination of the cyclometalated platinum complex <b>I</b> with a cationic surfactant allows for the detection of chloride in the micromolar concentration range in samples of bottled mineral water.