Charge-Density Induced Discrimination of Halides with a Rigid Dinuclear Copper(II) Complex

A rigid dinuclear copper(II) complex L based on furan spacers has been synthesized and studied for its binding interactions with halides by colorimetric studies, UV-Vis titrations, and density functional theory (DFT) calculations. Our results from the titration studies demonstrate that L binds each of the halides in the order of fluoride > chloride > bromide > iodide, correlating directly with the charge density of the respective halide. Fully unconstrained DFT geometry optimizations have been carried out on both the isolated L as well as the anion-bound motifs. Binding energies (DE) were calculated for each of the optimized geometries, yielding an attractive DE of -92.39, -27.14, -23.16, and -13.37 kcal/mol for fluoride, chloride, bromide, and iodide, respectively, which is in accord with our experimental results. The compound has been further investigated for its biocompatibility on HeLa cells, demonstrating an excellent cell viability up to 500 µM concentration.