Modulating the Sensor Response to Halide Using NBD-Based Azamacrocycles

Ligand L (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. L passes through the cellular
membrane, becoming fluorescent inside cells. The H–1L– species
is able to form dinuclear complexes with [M2H–1L]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–1L)­Cl2]­(ClO4)·4H2O is discussed. The Zn­(II) complex behaves as an OFF–ON
sensor for fluoride and chloride anions.