Multiple Sulfonation of Picolyl-Based Complexes Rendering Them Highly Water-Compatible.

Multidentate ligands chosen for the complexation of hard metals frequently exhibit negative charges, which consequently elicits Coulombic compensation of the metal-ion charge. However, ligands favored by soft metal ions are neutral, which prevents the chemist from obtaining electroneutral complexes, let alone ones with a negative total charge. Here, we report on an efficient synthetic method to decorate picolyl-displaying coordination compounds with multiple sulfonate units at their periphery. We further describe rare anionic versions of three standard complexes that have only been characterized as cationic so far. Our sulfonated complexes show extensive water solubility, which confers these species with great potential for broad application in the biomedical arena.