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

Abstract

The complexation behavior of diazophenylcalix[4]arene bearingpara-ethylester group (p-EAC) for alkali, alkaline earth, various heavy and transition metal ions (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Cr3+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+) was investigated by spectrophotometric and electrochemical methods in CH3CN center dot p-EAC exhibits decreased absorbance at 353 nm in the presence of Cr3+, Fe2+, Pb2+, and Cu2+. The spectra of p-EAC showed bathochromic shift in absorption maximum on the addition of Cr3+, Fe2+, or Pb2+ with decreasing order of absorbance (Cr3+ > Fe2+ > Pb2+), and on the other hand, hypsochromic shift on the addition of Cu2+. This leads to the selective coloration from light green to orange and colorless for Cr3+ and Cu2+ that can be detected by the naked eye, respectively. In electrochemistry experiments, p-EAC also showed two different types of voltammetric changes toward Cr3+, Fe2+, or Pb2+, and toward Cu2+, 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 Cr3+, Fe2+, Pb-2+,Pb- and Cu2+, respectively. (C) 2017 Elsevier B.V. All rights reserved.