Azo-methoxy-calix[4]arene complexes with metal cations for chemical sensor applications: Characterization, QTAIM analyses and dispersion-corrected DFT- computations

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.

Theoretical assessment of calix[4]arene-N-β-ketoimine (n=1-4) derivatives: Conformational studies, optoelectronic, and sensing of Cu2+cation

Herein, we have investigated the key functions of the calix[4]arene, abbreviated as CX [1], and designed its several derivatives by substitution of the functional groups. Molecular geometry provides an intuitive understanding of the effect of functional groups on various physical properties. The addition of the N-β-ketoimine (n = 1-4) ligands has a direct effect on the stretching vibration of the H-bonding interaction. The results showed that all molecules possess absorption bands at 190 nm and in the range between 200 and 300 nm assigned to π-π* and n-π* transitions. HOMO-LUMO energy gap of the CX[4]-N-β-ketoimine, one with chemical hardness of 1.62 eV, has been found to be 3.24 eV calculated at B3LYP/6-31 + G(d) level of theory. This finding explains the good kinetic stability of this compound. The large values of electrophilicity make the current molecules as a good electrophilic species. The atom in molecule (AIM) and the reduced density gradient (RDG) analyses showed the type and the strength of the interactions taking place between Cu²⁺ and the β-ketoimine ligands.