Synthesis and kinetics of photochromic carboxy-substituted dithizonatophenylmercury(II)

Abstract

With the aim of improving water-solubility and providing anchor points for follow-up reactions, the well-known intensely colored green analytical reagent, dithizone (H2Dz), was functionalized by two carboxylic acid substituents. Similarly, sulfacetamide and sulfonyl substituents were also employed, but its dithizone products decomposed in aqueous medium. The crystal structure of the nitroformazan carboxylic acid intermediate is reported. Its bent conformation is maintained by intramolecular hydrogen-bonding. Together with the two added dithizone carboxylate end groups the three spatially removed points are now available for complexation, eg. with phenylmercury(II) moieties. As opposed to the otherwise single-metal PhHgHDz(COOH)2 complex, added heavy mercury atoms in PhHgHDz(COOHgPh)2 inhibit photochromism in the tri-metallic complex. Kinetic studies of the photochromic return reaction of PhHgHDz(COOH)2 show the reaction rate to be linearly dependant on concentration and exponentially dependant on temperature, with rate constant of 0.0084 s−1 at 0 °C, i.e. four times faster than observed for the unsubstituted complex, PhHgHDz.