Molecular Modeling of 4-Ethyl-1-(pyridin-2-yl)thiosemicarbazide and its Cu(II) Complex Utilized for Separation of Cu(II) from Water Samples

Molecular modeling and spectroscopic characterization of 4-ethyl-1-(pyridin-2-yl) thiosemicarbazide (HEPTS) and its complex [Cu-4(EPTS)(3)(H2O)(EtOH)(OH)Cl-4](2)H2O are investigated. Structural, electronic, and vibrational features are discussed, and assignments were proposed on the basis of semiempirical quantum mechanics calculations (ZINDO/S and PM3). The simulated IR and UV-vis spectra are in reasonable accordance with the experimental data. Moreover, a rapid and selective procedure for extraction of Cu(II) at trace levels using silica gel immobilized with 4-ethyl-1-(pyridin-2-yl)thiosemicarbazide is proposed. The Cu(II)-EPTS complex was easily adsorbed on silica gel and eluted with 5.0 M HNO3. The pH, amount of HEPTS, sample volume, and detection limit were evaluated in synthetic, spiked, and tap water samples. The interfering effect of some cations and anions on the recovery of Cu(II) was studied. Under optimum conditions, the recovery of Cu(II) ions was (97 +/- 1) % at the 95 % confidence level. The adsorption isotherm was studied, and the binding equilibrium constant and the adsorption capacity were 3.585 L center dot mg(-1) and 520.8 mu g center dot g(-1), respectively. The detection limit and relative standard deviation were 4 ng center dot L-1 and 1.5 %, respectively. The proposed method was applied for the separation of Cu(II) ions from water samples.