| Abstract
| - A series of upper-rim p-allyl and p-methoxyphenylazocalix[4]arenes (6, 8, 9a,b, and 10a,b) weresynthesized and shown to exhibit substantial color changes upon complexation with Hg2+ ion. Both theupper-rim p-allyl- and p-methoxyphenylazo groups on calix[4]arenes are proven to be key componentsin the recognition of Hg2+ ion. Job's plots revealed 1:1 binding stoichiometry for all these p-allyl- andp-arylazo-coupled calix[4]arenes with Hg2+ ions and Benesi−Hilderbrand plots were used for determinationof their association constants. Our results also demonstrated that two p-methoxyphenylazo groups preferto bind Hg2+ in a distal orientation rather than a proximal one, and if there are three p-methoxyphenylazogroups, the third flanking p-methoxyphenylazo group plays a role in disturbing the binding of the twodistal diazo groups. Furthermore, it should be noted that triazocalix[4]arenes (6, 9a, and 9b) respondedto all 14 metal ions without showing much preference among the eight transition-metal ions screened inthis work (Cr3+, Ni2+, Cu2+, Ag+, Cd2+, Hg+, Hg2+, and Pb2+).
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