A series of new, octadentate, fluorescent, macrocyclic ligands have been prepared with a view to using them to study aromatic anion sequestration. The eight-coordinate Cd(II) complexes of the ligands have been shown capable of acting as receptors for a range of aromatic oxoanions. This has been demonstrated by perturbation of both 1H NMR chemical shift values and the anthracene derived fluorescence emission intensity as the potential guest anion and the host are combined. Non-linear least squares regression analysis of the resulting titration curves leads to the determination of binding constants in 20% aqueous 1,4-dioxane which lie in the range 10^2.3 M-1 (benzoate) to 10^7.5 M-1 (2,6-dihydroxybenzoate). By reference to the X-ray determined structures of related, but non-fluorescent inclusion complexes, the primary anion retention force is known to arise from hydrogen bonding between the anion and four convergent hydroxy groups that exist at the base of a cavity that develops in the complexes as their aromatic groups juxtapose upon coordination. This work reveals significant stability enhancement when hydroxy groups are positioned on the anion at points where O-H...pi hydrogen bonding to the aromatic rings that constitute the walls of the cavity becomes geometrically possible.
| Identifer | oai:union.ndltd.org:ADTP/216376 |
| Date | January 2007 |
| Creators | Bradbury, Adam John, babradbury@optusnet.com.au |
| Publisher | Flinders University. School of Chemistry Physics and Earth Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.flinders.edu.au/disclaimer/), Copyright Adam John Bradbury |
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