Synthetic and Structural Studies of a Linear Bis-Catechol Amide, N,N'-Bis(2,3-dihydroxybenzoyl)-1,7-diazaheptane (5-LICAM), and Its Complexes with Ni2+ and Co2+: Utilization of a Polymer-Supported, Sulfonated Analog, 5-LICAMS, as a Biomimetic Ligand for Divalent Metal Ion Removal from Aqueous Solution

Abstract

The synthesis and structural characterization of the linear bis(catechol) amide ligand, N,N{prime}-bis(2,3-dihydroxy-benzoyl)-1.7-diazaheptane (5-LICAM, 1), was studied along with several metal complexes, namely, Ni{sup 2+} and Co{sup 2+}. In order to test the utilization of 1 in removing Ni{sup 2+} from aqueous solution for environmental inorganic applications, the authors synthesized the polymer pendant ligand version, PS-5-LICAM, bonded to modified 6% macroporous divinylbenzene-polystyrene beads (0.55 mmol/g), with an important modification of a sulfonate group on the catechol ring, PS-5-LICAMS, to impart hydrophilicity to the ligand site. Indeed, it was found that the PS-5-LICAMS ligand removed 0.35 mmol of Ni/g of polymer beads from aqueous solution at pH 2.5, but unfortunately, was not selective to Ni{sup 2+} in competition with other divalent metal ions. An in depth discussion of the X-ray structure of ligand 2 and that of the Ni complex, 3, will be presented.