Allosteric anion recognition by metal complexation of tris(bipyridine–imidazolium) ligand

A new tripodal imidazolium ligand 2 comprising three 2,2′-bipyridine–imidazolium subunits connected through a mesityl spacer has been synthesized and 1:1 complexes of 2 with Fe(II) and Ru(II) ions have been prepared. 1H NMR spectroscopy including NOE analysis and molecular modeling study established that the complexes exist as a pseudocryptand type twisted structure in solution. The Fe(II) and Ru(II) complexes show strong 1:1 binding of Cl−, Br−, and I− anions in MeCN-d3 with a large enhancement of the guest selectivity (Cl− > Br− > I−) upon metal complexation.