Spectrophotometric and electrochemical study for metal ion binding of azocalix[4]arene bearing p-ethylester group.

The complexation behavior of diazophenylcalix[4]arene bearing para-ethylester group (p-EAC) for alkali, alkaline earth, various heavy and transition metal ions (Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Cr, Fe, Co, Ni, Cu, Zn, Pb) was investigated by spectrophotometric and electrochemical methods in CHCN. p-EAC exhibits decreased absorbance at 353nm in the presence of Cr, Fe, Pb, and Cu. The spectra of p-EAC showed bathochromic shift in absorption maximum on the addition of Cr, Fe, or Pb with decreasing order of absorbance (Cr>Fe>Pb), and on the other hand, hypsochromic shift on the addition of Cu. This leads to the selective coloration from light green to orange and colorless for Cr and Cu that can be detected by the naked eye, respectively. In electrochemistry experiments, p-EAC also showed two different types of voltammetric changes toward Cr, Fe, or Pb, and toward Cu, whereas no significant changes occurred in the presence of the other metal ions. Nonlinear fitting curve procedure was used to determine a logarithmic value of 5.20, 4.92, 3.54 and 4.80 for the stability constants of the complex of p-EAC with Cr, Fe, Pb, and Cu, respectively.