Thiomethoxychalcone-functionalized ferrocene ligands as selective chemodosimeters for mercury(II): single-crystal X-ray structural signature of the [Hg<SUB>8</SUB>(μ<SUB>8</SUB>-S)(SCH<SUB>3</SUB>)<SUB>12</SUB>]<SUP>2+</SUP>cluster

Thiomethoxychalcone-based ligands bis[3,3-bis(methylsulfanyl)]-1,1′- η<SUP>5</SUP>-ferrocenyl-2-propen-1-one (L1), 3,3-bis(methylsulfanyl)-1-η<SUP>5</SUP>-ferrocenyl-2-propen-1-one (L<SUP>2</SUP>), and 3-methylsulfanyl-3-sulfanyl-1-η<SUP>5</SUP>-ferrocenyl-2-propen-1-one (L<SUP>3</SUP>) 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<SUP>1</SUP> were obtained as both syn and anti conformers and showed the conformational freedom of the two cyclopentadienyl (Cp) units. L<SUP>1</SUP>−L<SUP>3</SUP> 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<SUP>1</SUP> and L<SUP>2</SUP> showed selective colorimetric sensing for Hg<SUP>2+</SUP> over Li<SUP>+</SUP>, Na<SUP>+</SUP>, Ca<SUP>2+</SUP>, Mg<SUP>2+</SUP>, Cr<SUP>2+</SUP>, Mn<SUP>2+</SUP>, Fe<SUP>2+</SUP>, Co<SUP>2+</SUP>, Ni<SUP>2+</SUP>, Cu<SUP>2+</SUP>, Zn<SUP>2+</SUP>, Cd<SUP>2+</SUP>, and Au<SUP>3+</SUP> in acetonitrile. In both cases, a selective color change from orange to purple was observed with Hg<SUP>2+</SUP> and the resultant solution showed the appearance of a new peak at 565 nm (ε = 3920 M<SUP>−1</SUP> cm<SUP>−1</SUP>) for L<SUP>1</SUP> and 600 nm (ε = 1140 M<SUP>−1</SUP> cm<SUP>−1</SUP>) for L<SUP>2</SUP> in the UV/vis experiments. The UV/vis titration profiles of L<SUP>1</SUP> and L<SUP>2</SUP> indicate the formation of 2:1 (L<SUP>1</SUP>/Hg<SUP>2+</SUP>) and 1:1 (L<SUP>2</SUP>/Hg<SUP>2+</SUP>) initial complexations in solution. On the other hand, L<SUP>3</SUP> with thiomethoxy- and thiol-functionalized ferrocenylchalcone showed no appreciable color change with Hg<SUP>2+</SUP> under the same experimental conditions. Attempts were made to isolate single crystals of the resulting purple solution obtained in the cases of L<SUP>1</SUP> and L<SUP>2</SUP> with Hg<SUP>2+</SUP>. 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<SUB>8</SUB>S(SCH<SUB>3</SUB>)<SUB>12</SUB>]<SUP>2+</SUP>, upon a selective chemodosimetric desulfurization reaction between Hg<SUP>2+</SUP> and L<SUP>1</SUP> or L<SUP>2</SUP>. Cyclic voltammetric studies also support the Hg<SUP>2+</SUP>-induced cleavage of thiomethoxy groups