Comparative density functional theory study on thiacalix[4]arene binding modes for Zn2+ and Cu2+

Area of Science:

• Supramolecular Chemistry
• Computational Chemistry
• Coordination Chemistry

Background:

• Thiacalix[4]arene macrocycles are versatile platforms for metal ion complexation.
• Understanding metal-ligand interactions is crucial for designing selective metal chelators.

Purpose of the Study:

• To comparatively investigate the complexation of zinc (II) and copper (II) ions with thiacalix[4]arene.
• To elucidate the structural and energetic factors governing metal-ligand binding modes.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Analysis of structures, energetics, and electrostatic potential surfaces of metal complexes.

Main Results:

• Two binding patterns (adjacent or opposite phenolate groups) were identified in deprotonated thiacalix[4]arene species.
• A novel, highly stable distorted square planar coordination was predicted for both Zn(2+) and Cu(2+) at the lower rim with opposite phenolate groups.
• Copper (II) demonstrated a higher complexation ability than zinc (II) across all binding modes.

Conclusions:

• The study identified a previously unreported stable binding mode for metal-thiacalix[4]arene complexes.
• Differential charge transfer explains the superior complexation of Cu(2+) over Zn(2+).
• Findings align with experimental observations from liquid-liquid extraction studies.