| dc.description.abstract | Amongstthe countless man-made contaminants that infiltrate our water sources are heavy metals, usually as by-products of industrial processes. Many metals, particularly heavy metals are toxic. Metal contamination (e.g, Hg, Pb, Cd, etc.) can\be addressed by using filters/sorbents (e.g. gamma alumina), and flocculation/precipitation,1mt these methods are non-specificand best suited to contaminants at high concentrations. Chelating extraction is a potential technology of remediation for heavy metals-contaminated water and as such considerable attention has been devoted to the development of chelating agents for liquidliquid extraction of metal ions. The ligands 2,6-bis(pyrazol-I-ylmethyl)pyridine (LI), 2,6bis(3,5-dimethylpyrazol-I-ylmethyl)pyridine (L2), 2,6-bis(3,5-ditertbutylpyrazol-lylmethyl)pyridine (1..3), 2-(pyrazoI-I-ylmethyl)pyridine (IA), 2-(3;5-dimethylpyrazol-lylmethyl)pyridine (L5) and 2-(3,5-ditertbutylpyrazol-I-ylmethyl)pyridine (L6) were prepared and their coordination chemistry with zinc and cadmium metal ions investigated prior to their applications as chelating agents to remove heavy metals from water. Ligands L2, L5 and L6 reacted with either Zn(N03~, ZnCh, Cd(N03)2 or CdCh to form monometallic complexes [Zn(NOl~{L5)] (CI), [Zn(NOl~(L6)] (C2), [ZnCb(LS)] (C3), [Cd(N03)2(L5)] (C4), [Cd(NOlh(L6)] (CS), [CdCh(L5)] (C6), [Zn(N03)2(L2)] (C7), [ZnCb(L2)] (C8), [Cd(N03h{L2)] (C9), (CdCb{L2)] (CIO). All the new compounds prepared were characterized by IH NM:R.and elemental analyses. Single crystal X-ray crystallography of complexes CI, Cl, C4, CS, C7 and C9 has been used to confirm the solid state structure of the complexes. L5 and L6 adopts bidentate coordination mode through the pyridine nitrogen and one pyrazolyl nitrogen atom as confrrmed by single crystal X-ray crystallography of complexes Ct, 0, C4 and CS. The tridentate coordination ofL2 has also been established by the solid state structures ofC7 and C9. The abilities of 2,6-bis(pyrazol-I-ylmethyl)pyridine (Lt), 2,6-bis(3,5-dimethylpyrazol-I-ylmethyl)pyridine (L2), 2,6-bis(3,5-ditertbutylpyrazol-I-ylmethyl)pyridine (LJ), 2-(pyrazol-lylmethyl)pyridine (U), and 2-(3,5-dimethylpyrazol-I-ylmethyl)pyridine (LS) to extract heavy metal ions, (lead(ll), cadmium(Il) and zinc(Il) were examined by liquid-liquid extraction experiments using dichloromethane-water biphasic system Extraction efficiency was found to be dependent on the type of metal cations. All the ligands showed greater extraction efficiency for zinc (88-99%) and lowest extraction for cadmium (19-31%). The ligand architecture as well as experimental conditions such as metal:ligand ratio, time of reaction influenced the extraction efficiency of the ligands. Theoretical studies using Density Functional Theory by Gassian03 have been used to explain the observed experimental trends.The theoretical results were consistent with the experimental results , with zinc(ll) giving the highest negative enthalpy followed by le~(ll) and cadmium(II) giving the lowest. | en_US |
