Self-assembly of a metal-ion-bound monolayer of trigonal connectors on mercury: An electrochemical Langmuir trough

The adsorption of the trigonal connector, 1,3,5-tris[10-(3-ethylthiopropyl)dimethylsilyl-1,10-dicarba-closo-decaboran-1-yl]benzene (1), from acetonitrile/0.1 M LiClO(4) on the surface of mercury at potentials ranging from +0.3 to −1.4 V (vs. aqueous Ag|AgCl|1 M LiCl) was examined by voltammetry, Langmuir isotherms at controlled potentials, and impedance measurements. No adsorption is observed at potentials more negative than ∼ −0.85 V. Physisorption is seen between ∼ −0.85 and 0 V. At positive potentials, adsorbate-assisted anodic dissolution of mercury occurs and an organized surface layer is formed. Although the mercury cations are reduced at −0.10 V, the surface layer remains metastable to potentials as negative as −0.85 V. Its surface areas per molecule and per redox center are compatible with a regular structure with the connectors 1 woven into a hexagonal network by RR′S→Hg [Formula: see text] ←SRR′ or RR′S→Hg(2+)←SRR′ bridges. The structure is simulated closely by geometry optimization in the semiempirical AM1 approximation.