Thorium Bis-Salophen Trimers as Anion Detectors and Binding Agents

Bis-salophen ligands are the condensation product of a tetramine and a salicylaldehyde derivative. They feature two binding sites, both of which are tetradentate with mixed O/N donor atoms. Reaction with the ligand precursor and thorium nitrate tetrahydrate forms a 3:3 metal-to-ligand trimer with a ΔΔΔ-chirality confirmed by X-ray crystallography of a racemic single crystal. The structure has a pore in the center of the triangular structure measuring 6.22 Å at its narrowest point. This compound is air- and water-stable as well as soluble in organic solvents. This compound was screened with a series of tetrabutyl ammonium halide salts, and tetrabutylammonium (TBA) chloride showed the strongest binding to the complex. After the addition of 2 equivalents of TBACl, the complex and salt precipitate out of solution.