Complexation, extraction, and sensing of Hg(II) by sulfonamide ligands derived from o-phenylenenediamine

Mercury (Hg) separation and sensing is of significance due to Hg(II) environmental mobility and toxicity. Furthermore, the use of Hg in nuclear applications has resulted to its accumulation in several DOE sites, such as in Oak Ridge and Savannah River reservations.
Three bis-arylsulfonamide ligands (L₁, L₂, and L_D) derived from substituted o-phenylenediamine and several sulfonyl chlorides (Figure - left) have been synthesized and tested for extraction, and sensing of Hg(II). These bidentate ligands act as N-donors that coordinate to Hg(II) through the amine group after deprotonation. Successful extraction of Hg(II) from alkaline aqueous phases into dichloroethane was observed with extraction efficiency and recovery as high as 97.4 % and 81.5 % respectively at pH 12.0 by L₂. The influence of pH, ligand concentration, and the presence of the organic bases triethylamine or diisopropylethylamine (DIPEA) was studied in detail. Slope analysis of the extraction experiments at pH 12.0 showed a 1:2 Hg(II):L₂ complex stoichiometry in the presence of triethylamine and 1:1 complex in the absence of triethylamine. The crystal structure of the isolated Hg(II) complex with L₁ (Figure - right) shows a 1:2 Hg(II):L₁ stoichiometry with two triethylammonium countercations (Et₃NH⁺) coordinating in the outer sphere. The bis-dansylsulfonamide ligand (L_D) was shown to be an effective Hg(II) sensor, as fluorescence quenching was observed upon gradual addition of HgCl₂ solution with complete quenching at 1:1 Hg(II):L_D ratio. L_D was also shown to extract Hg(II) from aqueous phases into dichloroethane in the presence of DIPEA, with extraction efficiency as high as 99.2 %.

Bis-arylsulfonamide ligands studied (left). X-ray structure of the isolated Hg(II) complex with L₁ (right).