Modulating the Sensor Response to Halide Using NBD-Based Azamacrocycles

Ligand <b>L</b> (2,6-bis­{[7-(7-nitrobenzo­[1,2,5]­oxadiazole-4-yl)-3,10-dimethyl-1,4,7,10-tetraazacyclododeca-1-yl]­methyl}­phenol) is a fluorescent sensor that is useful for detecting Cu­(II), Zn­(II), and Cd­(II). Some of the complexes formed are able to sense the presence of halides in solution. <b>L</b> passes through the cellular membrane, becoming fluorescent inside cells. The H_<i>–</i>1<b>L</b>^<i>–</i> species is able to form dinuclear complexes with [M₂H_<i>–</i>1<b>L</b>]³⁺ stoichiometry with Cu­(II), Zn­(II), and Cd­(II) ions, experiencing a CHEF effect upon metal coordination in an acetonitrile/water 95:5 (v/v) solution. In all three of the complexes investigated, the metal cations are coordinatively unsaturated and can therefore bind secondary ligands as anionic species. The crystal structure of [Cd₂(H_<i>–</i>1<b>L</b>)­Cl₂]­(ClO₄)·4H₂O is discussed. The Zn­(II) complex behaves as an OFF–ON sensor for fluoride and chloride anions