Synthesis and structural studies of metal complexes of the biological ligand 2-quinaldic acid: Utilization of the polymer pendant analog PS-2-QA for selective aluminum ion removal from aqueous solution

The synthetic reactions of quinaldic acid (2-QA, 1), a ligand with potential implications in Al3+ ion biological transport and in pharmaceutical applications and of use for the removal and recovery of Al3+ ions from environmental waste sites, were studied with tri- and divalent metal ions that-encompass Al3+, Fe3+, Ga3+, Zn2+, Ni2+, Mn2+, and Co2+. The Al3+, Fe3+, and Ga3+ metal ion complexes, 2-4, of 1 were characterized by FT-IR, FAB/MS, NMR, and elemental analysis and provided the following structural formula with 1 of 2-QA(4)M(2)(mu-OH)(2) . S, where S = H2O or pyridine. In the case of the Ga3+ analog, 4 . Py, the unequivocal mu-OH dimer structure was determined by single-crystal X-ray analysis [space group, P1; a = 13.387(3) Angstrom; b = 14.016(2) Angstrom; c = 14.549(2) Angstrom; alpha = 87.74(2)degrees; beta = 73.44(2)degrees; gamma = 82.61(2)degrees; Z = 2; volume = 2592.6 Angstrom(3)]. A description of the X-ray crystal structure of 2-QA(4)Ga(2)(mu-OH)(2) . 4 pyridine, 4 . Py, will also be presented. The corresponding bis(2-QA) metal complexes of Zn2+, Ni2+, Mn2+, and Co2+, 5-8, were also studied and all provided a formula of 2-QA(2)M . 1.5 H2O, which were also characterized by many of the above-mentioned spectroscopic techniques. The polymer-supported (PS) version of 1, PS-2-QA, bonded to modified, macroporous 6% cross-linked polystyrene-divinylbenzene beads, was synthesized by an electrophilic substitution reaction on the aromatic ring of a 2-QA derivative, ethyl 2-quinaldate, with the chloromethylated precursor, PS-CH2Cl, followed by subsequent ester hydroysis to the free PS-2-QA ligand. The PS-2-QA ligand was found to selectively remove Al3+ ions from aqueous acidic solution (pH = 3-5) in the presence of other divalent metal ions, namely, Cu2+ Zn2+, Ni2+, Mn2+, and Co2+ as well as a trivalent metal ion, Cr3+.