A theoretical insight into several common anion recognitions based on double-dentate hydrogen bond and anion-π coexistence

Anion recognitions of a pincer-like receptor (N,N'-bis-(2-fluoro-benzoyl-oxyethyl)-urea, AR) for several common inorganic anions (F-, Cl-, Br-, I-, CN-, and SO42-) were theoretically explored and predicted at a molecular level in this paper. Geometric configurations of the complex (AR@X (X = F-, Cl-, Br-, and SO42-)) show that two N-H groups as a claw and two-C6H4F rings on AR as a pair of tweezers simultaneously interact with the captured anions through cooperative double-dentate hydrogen bond and double-side anion-p interactions. However, there is no anion-p contact between AR and I-ion in AR@I-complex. In the system of AR@CN-, a stable single-side CN--pi is possible. The structure of stable 2:1 complex formed with two AR receptors and one SO42- is also predicted. The binding energies and thermodynamic information indicate that the recognitions of the above six anions by AR in the vacuum are spontaneously enthalpy-driven and entropy-opposed. The binding energy Delta E-cp between SO42- and AR is higher than 340 kJ mol(-1), suggesting that AR is an ideal selective anion receptor for SO42-. Additionally, energy decomposition analysis based on localized molecular orbital energy decomposition analysis (LMO-EDA) was performed. Electronic properties and behaviors of the present systems were further discussed according to calculations on frontier molecular orbital, UV-vis spectra, and visualized weak interaction regions.