Maoqun Tian, H. Ihmels
Aug 1, 2011
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0
Influential Citations
19
Citations
Journal
European Journal of Organic Chemistry
Abstract
1,4-Dioxa-7,13-dithia-10-azacyclopentadecane (AT215C5) or 1,4,7,10-tetraoxa-13-azacyclopentadecane (A15C5) were attached as metal-ion-binding receptor units at the ortho or para positions of the 9-amino-N-phenylbenzo[b]quinolizinium chromophore. The addition of Hg2+ or Mg2+ to the para isomers of the AT215C5–quinolizinium or A15C5–quinolizinium conjugate, respectively, led to a blueshift of the absorption maxima of each compound because of the reduced donor ability of the complexed amino group. In contrast, the addition of Hg2+ to a solution of the ortho-AT215C5–quinolizinium conjugate in H2O/MeOH mixtures induced a significant redshift (ca. 50 nm) of the absorption maximum and enabled the photometric discrimination between Hg2+ and competing thiophilic cations, such as Ag+ or Pb2+, because the latter, as well as other competing metal ions, did not induce such an effect. It is proposed that the Hg2+-induced redshift originates from the complexation of Hg2+ by the thiaazacrown ether followed by deprotonation of the secondary 9-amino substituent of the aminobenzoquinolizinium unit. The resulting amide functionality increases the donor–acceptor interplay leading to the redshifted absorption and also coordinates to Hg2+ to form a lariat ether type complex. A similar effect was observed upon the addition of Mg2+ to the 9-amino-N-phenylbenzo[b]quinolizinium derivative with the A15C5 unit in the ortho position; however, this effect was only operative in aprotic solvents, e.g. CH3CN, and with less than 1 mol-equiv. of Mg2+.