Cation-Selective and Anion-Controlled Fluorogenic Behaviors of a Benzothiazole-Attached Macrocycle That Correlate with Structural Coordination Modes

We
report how the metal cation and its counteranions cooperate
in the complexation-based macrocyclic chemosensor to monitor the target
metal ion via the specific coordination modes. The benzothiazolyl
group bearing NO2S2-macrocycle L was synthesized, and its mercury­(II) selectivity (for perchlorate
salt) as a dual-probe channel (UV–vis and fluorescence) chemosensor
exhibiting the largest blue shift and the fluorescence turn-off was
observed. In the mercury­(II) sensing with different anions, except
ClO4– and NO3–, no responses for mercury­(II) were observed with other anions such
as Cl–, Br–, I–, SCN–, OAc–, and SO42–. A crystallographic approach for the mononuclear
mercury­(II) perchlorate complex [Hg­(L)­(ClO4)2]·0.67CH2Cl2 (1) and polymeric mercury­(II) iodide complex [Hg­(L)­I2]n (2) revealed
that the observed anion-controlled mercury­(II) sensing in the fluorescence
mainly stems from the endo- and exocoordination modes, depending on
the anion coordinating ability, which induces either the Hg–Ntert bond formation or not. The detailed complexation process
with mercury­(II) perchlorate associated with the cation sensing was
also monitored with the titration methods by UV–vis, fluorescence
spectroscopy, and cold-spray ionization mass spectrometry.