Optical spectroscopy studies of the complexation of bis(azophenol)calix[4]arene possessing chromogenic donors with Ni2+, Co2+, Cu2+, Pb2+ and Hg2+

Due to their potential applicability as selective receptors in electrochemical or optical sensors, a bis(azophenol)calix[4]arene derivative H2L has been investigated. The complexation properties of this molecule towards Ni2+ and Co2+ metal ions has been studied. It is revealed that this ligand exhibits tetradentate with N2O2 core when bound to Ni (II) or Co (II) metal ion. The optical response of azo groups of H2L towards Ni2+, Co2+, Cu2+, Pb2+ and Hg2+ metal ions has been investigated in DMSO by UV–vis spectroscopy. The absorption spectra of calix[4]arene with cations show marked changes, especially for Co2+ ion. Furthermore, Job’s plot indicate 1:1 binding-stiochiometry for calix[4]arene with Co2+ ion and Benson-Hilderbrand plot is used for the determination of its association constant. The investigation of UV–vis spectra of chromogenic calix[4]arene in different solvents shows that cis–trans isomerization of azo groups probably depends on kind of solvent. Also the different between the polarity and viscosity of organic solvents used is likely responsible for the changes of the band shape of the spectra.

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► We explored interaction between some M2+ metal ions and bis(azophenol)calix[4]arene H2L in DMSO.
► The absorption spectra of calix[4]arene with cations show marked changes, especially for Co2+ ion.
► Job’s plot indicated 1:1 binding-stoichiometry for calix[4]arene with Co2+ ion.
► 1:1 association constant of H2L with Co2+ is determined on the base of Bensi-Hilderbrand plot at λ = 317 nm.
► It is revealed that the stability constant of calix[4]arene H2L with cobalt is Ka = 2.40 × 104 M−1.