Hg(II) sensing properties of (diphosphine)Pt(dmit) complexes (dmit: C3S52 −: 1,3-dithiole-2-thione-4,5-dithiolate)

Heteroleptic chelate complexes with a [P2PtS2] core, (dppf)Pt(dmit) (1) and (dppe)Pt(dmit) (2), where dppf is 1,1′-bis(diphenylphosphino)ferrocene and dmit is 1,3-dithiole-2-thione-4,5-dithiolate, were shown to exhibit colorimetric sensing properties for the Hg(II) ion. The absorption peak for the π → π* transition of the Cdouble bond; length as m-dashS moiety in the dmit ligand observed at 464 nm (ε = 1.2 × 104 M− 1 cm− 1) showed a bathochromic shift to 537 nm (ε = 0.8 × 104 M− 1 cm− 1) as [Hg(II)]/[1] was increased up to 300, which was accompanied by color change from yellow to purple. These changes resulted from the binding of Hg(II) ions to the Cdouble bond; length as m-dashS moiety. The affinity of (1) and (2) toward Hg(II) ion was estimated as Kd = 5.74 (± 0.40) × 10− 3 M for (1) and Kd = 5.60 (± 0.38) × 10− 3 M for (2). The metal- and dithiolate-substitutes of compound (1), (dppf)Ni(dmit) (3) and (dppf)Pt(bdt) (4) where bdt is 1,2-benzenedithiolate, showed no Hg(II)-sensing ability due to the instability of (3) in solution and a lack of a Hg(II)-binding site for (4). The Hg(II)-sensing selectivity for (1) and (2) was also confirmed when compared to other metal ions, such as Cr(III), Fe(II), Co(II), Cu(II), Zn(II) and Ag(I).