Halogen bond interactions enhanced by sodium bonds — Theoretical evidence for cooperative and substitution effects in NCX···NCNa···NCY complexes (X = F, Cl, Br, I; Y = H, F, OH)

Abstract

Quantum chemical calculations are performed to study cooperativity and substituent effects between halogen bond and sodium bond interactions in NCX···NCNa···NCY complexes, where X = F, Cl, Br, I and Y = H, F, OH. These effects are studied in terms of equilibrium geometry, interaction energy, 15N nuclear magnetic resonance (NMR) parameters, and electron density analysis of the complexes at the MP2/aug-cc-pVTZ level. The X···N and Na···N bond lengths in the ternary systems are always shorter than those in the corresponding dyads. In each triad, the decrease in the halogen bond length is far greater than that of the sodium bond. In all triads studied, a favorable cooperativity is found with values that range between –0.30 and –1.72 kcal/mol. It is revealed that NMR parameters at the site of the nitrogen atom of the NCNa molecule can be regarded as a good description to quantify the degree of cooperative effects in the NCX···NCNa···NCY systems. The nature of halogen bond and sodium bond interactions of the complexes is analyzed using parameters derived from the quantum theory of atoms in molecules methodology and energy decomposition analysis.