In silico exploration of O-H^…X²⁺ (X = Cu, Ag, Hg) interaction, targeted adsorption zone, charge density iso-surface, O-H proton analysis and topographic parameters theory for calix[6]arene and calix[8]arene as model

Abstract

In this work, the best adsorption targeted zones of the metal cations Ag2+, Cu2+ and Hg2+ at the surfaces or inside, outside the cavity of the calix[6] (CX[6]), calix[8]arene (CX[8]), NUBMOM (NUB-.) and LAYKUR (LAY-.) have been discussed. For X2+=Ag, Cu and Hg adsorbed onto the surface of CX[6,8], NUB-., and LAY-. and the morphologies of these complexes have been explained, the specific chosen surface structure has interfacial chemical properties to facilitate the stabilization of the cation in each targeted zone. The stability mechanisms have been investigated for the specific systems to understand the role of the cooperativity of the O…H (forming a donor-acceptor couple) bonding interactions for good selectivity to the cation in each host-guest in the acetonitrile solvent medium and the gas phase. For this purpose, all the host-guests chemical structures were investigated by the IR spectroscopy and O-H proton approach. The UV–visible absorption spectroscopy and the total DOS Orbital showed that all molecules possess a maximum absorption band in the range between 0.5 and 3.5 eV assigned to π–π* or n-π* transitions, the minimum band is characterized for the CX[6,8]-Cu2+, NUB-.Cu2+ and LAY-.Cu2+, while the highest band is specified for the complexation with the cation Ag2+. The Hirshfeld surface and the molecular electrostatic potential topography have demonstrated the selected targeted zone for the most stable configurations. The nature and the type of interaction formed between the chosen cation and the targeted area of the CX[6,8], NUB-. and LAY-. were typically studied by the Atom in Molecules (AIM) approach via non-covalent interaction (NCI) analyses. According to theoretical calculations, Cu2+, Ag2+ and Hg2+ cations were complexed with CX[6] and CX[8]-arenes in endo and exo-type form. In the endo complexes, it has been observed that Cu2+and Ag2+ cations enter the lower rim space where calixarene hydroxyl groups are located and form a complex in square planer geometry, as expected. This situation shows that the copper cation is planarly located in the calixarene core. These results show that the theoretical results are in good agreement with the experimental ones. In addition, our simulations point out the calix[6] arene and calix[8]arene were complexed with cations by “pinched” conformation, corresponding to best stable state.