Azo-methoxy-calix[4]arene complexes with metal cations for chemical sensor applications: Characterization, QTAIM...

In this work, the structures, quantum chemical descriptors, morphologic characterization of the azo-methoxy-calix[4]arene were investigated. The analyses and interpretation of the theoretical and the experimental IR spectroscopy results for the corresponding compounds was performed. The complexation of the azo-methoxy-calix[4]arene with Zn²⁺,Hg²⁺ , Cu²⁺ , Co²⁺, Ni²⁺ , Pb²⁺ and Cd²⁺metal cations has been calculated by the dispersion corrected density functional theory (DFT-D3). The values of the interaction energies show that the specific molecule is more selective to the Cu²⁺ cation. The study of the reactivity parameters confirms that the azo-methoxy-calix[4]arene molecule is more reactive and sensitive to the Cu²⁺ cation than that Co²⁺ and Cd²⁺. In addition, the investigation of the electrophilic and nucleophilic sites has been studied by the molecular electrostatic potential (MEP) analysis. The Hirshfeld surface (HS) analysis of the azo-methoxy-calix[4]arene-Cu²⁺ interaction have been used to understand the Cu⋯hydrogen-bond donors formed between the cation and the specific compound. The Quantum Theory of Atoms in Molecules (QTAIM) via Non covalent Interaction (NCI) analysis was carried out to demonstrate the nature, the type and the strength of the interaction formed between the Cu²⁺ cation and the two symmetrical ligands and the cavity. Finally, the chemical sensor properties based on the Si/SiO₂/Si₃N₄/Azo-methoxy-calix[4]arene for detection of Cu²⁺ cation were studied. Sensing performances are determined with a linear range from 10^-5.2 to 10^-2.2 M. The Si/SiO₂/Si₃N₄/azo-methoxy-calix[4]arene structure is a promoter to have a good performance sensor.