Thiomethoxychalcone-functionalized ferrocene ligands as selective chemodosimeters for mercury(II): single-crystal X-ray structural signature of the [Hg8(mu8-S)(SCH3)12]2+ cluster.
ABSTRACT Thiomethoxychalcone-based ligands bis[3,3-bis(methylsulfanyl)]-1,1'-eta(5)-ferrocenyl-2-propen-1-one (L(1)), 3,3-bis(methylsulfanyl)-1-eta(5)-ferrocenyl-2-propen-1-one (L(2)), and 3-methylsulfanyl-3-sulfanyl-1-eta(5)-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 Hg(2+) over Li(+), Na(+), Ca(2+), Mg(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Au(3+) in acetonitrile. In both cases, a selective color change from orange to purple was observed with Hg(2+) and the resultant solution showed the appearance of a new peak at 565 nm (epsilon = 3920 M(-1) cm(-1)) for L(1) and 600 nm (epsilon = 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)/Hg(2+)) and 1:1 (L(2)/Hg(2+)) initial complexations in solution. On the other hand, L(3) with thiomethoxy- and thiol-functionalized ferrocenylchalcone showed no appreciable color change with Hg(2+) 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 Hg(2+). 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, [Hg(8)S(SCH(3))(12)](2+), upon a selective chemodosimetric desulfurization reaction between Hg(2+) and L(1) or L(2). Cyclic voltammetric studies also support the Hg(2+)-induced cleavage of thiomethoxy groups.