Chemosensing of Chloride Based on a Luminescent Platinum(II) NCN Pincer Complex in Aqueous Media

2014-02-24T00:00:00Z (GMT) by Alejandro Dorazco-Gonzalez
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.