Re‐Evaluation of the Applicability of Terpyridine as a Highly Selective Aqueous Colorimetric Sensor for Mercury

In a more than 100‐times cited article published in Chem. Eur. J. in 2008 (reference [4]), 2,2´:6´2´´‐terpyridine ( tpy ) has been reported to be a “highly selective colorimetric aqueous sensor for mercury.” Verification of this message reveals that the key data and claims reported in the article [4] do not agree with reality. In aqueous DMSO, the reaction of Hg II compounds with tpy does not produce the pink species [Hg( tpy ) 2 ] 2+ , but white (colorless) products with limited solubility, uncertain stoichiometry and thus structure, and zero use in colorimetry. The color and spectra assigned in the article [4] to Hg II / tpy systems actually exhibit systems Fe II / tpy , so that tpy can potentially serve as a colorimetric aqueous sensor for Fe II ions with the naked‐eye detection limit of 1·10 −6 mol/L. Practically only Fe II mono‐ tpy species are present in solutions in DMSO( aq ) of conc. at least up to the 10 −2 mol/L.