Selective turn-off phosphorescent and colorimetric detection of mercury(II) in water by half-lantern platinum(II) complexes

The platinum(II) half-lantern dinuclear complexes [{Pt(bzq)(mu-C7H4NS2-kappa N,S)}(2)] (A) and [{Pt(bzq)(mu-C7H4NOS-kappa N,S)}(2)] (B) [bzq = benzo[h]quinolinate, C7H4NS2 = 2-mercaptobenzothiazolate, C7H4NOS = 2-mercaptobenzoxazolate] in solution of DMSO-H2O undergo a dramatic color change from yellowishorange to purple and turn-off phosphorescence in the presence of a small amount of Hg2+, being discernible by the naked-eye and by spectroscopic methods. Other metal ions as Ag+, Li+, Na+, K+, Ca2+, Mg2+, Ba2+, Pb2+, Cd2+, Zn2+ and Tl+ were tested and, even in a big excess, showed no interference in the selective detection of Hg2+ in water. Job's plot analysis indicated a 1 : 1 stoichiometry in the complexation mode of Hg2+ by A/B. The phosphorescence quenching attributed to the formation of [A/B : Hg2+] complexes showed binding constants of K = 1.13 x 10(5) M-1 (A) and K = 1.99 x 10(4) M-1 (B). The limit of detection has been also evaluated. In addition, dried paper test strips impregnated in DMSO solutions of A and B can detect concentration of Hg2+ in water as low as 1 x 10(-5) M for B and 5 x 10(-5) M for A, making these complexes good candidates to be used as real-time Hg2+ detectors. The nature of the interaction of the Pt-2 half-lantern complex A with the Hg2+ cation, has been investigated by theoretical calculations.