Interaction of bromine vapor with nitrogen-based electron-donor molecules: thermodynamic, kinetic, and DFT investigations.

CONTEXT: Molecular bromine (Br₂) is an important halogen in atmospheric chemistry and is also associated with environmental contamination. Nitrogen-containing donor molecules in methanolic solutions interact selectively with Br₂, leading to the formation of donor-bromine complexes. The diffusion and reactivity of bromine vapor were investigated using UV-visible spectroscopy in the 200-600 nm range. Bromine concentrations and reaction products were quantified through calibration curves and mathematical modeling. Photophysical and thermodynamic parameters, including molar extinction coefficients, absorption energies, equilibrium constants, and Gibbs free energy changes, were determined. Kinetic parameters for forward and reverse reactions were obtained using a pseudo-second-order model. These results confirm the formation of donor-bromine complexes and their potential for selective bromine capture.

METHODS: Quantum chemical calculations were performed to analyze the most representative donor-bromine complexes. All molecular structures, including the electron donor molecules (azobenzene, benzamide, benzylamine, and phenylhydrazine) and their bromine complexes, were constructed using Avogadro 1.95. Geometry optimizations and vibrational frequency analyses were carried out with Density Functional Theory (DFT) using the B3LYP functional with D3BJ dispersion corrections and the def2-TZVPP basis set, as implemented in ORCA 6.0.1. Methanol solvent effects were included using the CPCM model with SMD parameters, and tight SCF convergence criteria were applied. Multiple conformers were explored for each donor-bromine system, with the most representative conformer selected for analysis. Frontier molecular orbitals (HOMO and LUMO) were visualized using IBOView, and electronic descriptors including HOMO-LUMO gaps, interaction energies, Mulliken atomic charges, Mayer bond orders, and molecular dipole moments were obtained to provide electronic insights consistent with experimental observations.