Thiomethoxychalcone-Functionalized Ferrocene Ligands as Selective Chemodosimeters for Mercury(II): Single-Crystal X-ray Structural Signature of the [Hg8(μ8-S)(SCH3)12]2+ Cluster

Thiomethoxychalcone-based ligands bis[3,3-bis(methylsulfanyl)]-1,1′- η5-ferrocenyl-2-propen-1-one (L 1 ), 3,3-bis(methylsulfanyl)-1-η5-ferrocenyl-2-propen-1-one (L 2 ), and 3-methylsulfanyl-3-sulfanyl-1-η5-ferrocenyl-2-propen-1-one (L 3 ) have been synthesized on the ferrocene backbone by varying the number of chalcone arms and thiomethoxy substitutents. The single-crystal X-ray crystallographic analyses of all three ligands are reported in which crystals of L 1 were obtained as both syn and anti conformers and showed the conformational freedom of the two cyclopentadienyl (Cp) units. L 1 −L 3 are studied extensively toward their applicability in the colorimetric sensing of metal ions in solution. The solution-state study of mono- and bis(thiomethoxy)ferrocenylchalcone-functionalized ligands L 1 and L 2 showed selective colorimetric sensing for Hg2+ over Li+, Na+, Ca2+, Mg2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Au3+ in acetonitrile. In both cases, a selective color change from orange to purple was observed with Hg2+ and the resultant solution showed the appearance of a new peak at 565 nm (ε = 3920 M−1 cm−1) for L 1 and 600 nm (ε = 1140 M−1 cm−1) for L 2 in the UV/vis experiments. The UV/vis titration profiles of L 1 and L 2 indicate the formation of 2:1 (L 1 /Hg2+) and 1:1 (L 2 /Hg2+) initial complexations in solution. On the other hand, L 3 with thiomethoxy- and thiol-functionalized ferrocenylchalcone showed no appreciable color change with Hg2+ under the same experimental conditions. Attempts were made to isolate single crystals of the resulting purple solution obtained in the cases of L 1 and L 2 with Hg2+. In both cases, crystals suitable for a single-crystal X-ray diffraction study were isolated in very low yield by a layer diffusion technique. The single-crystal structural investigations demonstrated the formation of a sulfide-encapsulated mercury thiolate cuboctahedron cluster, [Hg8S(SCH3)12]2+, upon a selective chemodosimetric desulfurization reaction between Hg2+ and L 1 or L 2 . Cyclic voltammetric studies also support the Hg2+-induced cleavage of thiomethoxy groups.