Detecção e caracterização de ligações halógenas através de espectrofotometria UV-Vis e modelagem molecular

This study investigates halogen bonds (XBs) in bromine-acetone complexes (Br₂···Ac) using UV-Vis spectrophotometry and computational methods. Electronic structure calculations, including geometry optimizations and excited-state calculations, were carried out using the Gaussian 16 program. Time-Dependent Density Functional Theory (TD-DFT) method, with the M06-2X functional and def2-TZVP basis set, was employed to determine absorption energies corresponding to HOMO→LUMO transitions. Acetone solvation was simulated using the Polarizable Continuum Model (PCM). Experimental UV-Vis spectra of gaseous Br₂ revealed two absorption peaks at 238 nm (λ1,exp) and 454 nm (λ2,exp). Upon dissolution in acetone, λ2,exp underwent a hypsochromic (blue) shift, reaching 395 nm and 365 nm at 0.04 and 0.01 M Br2, respectively. This shift is attributed to XB formation, supported by theoretical spectra showing peaks at 390 nm (Br2···Ac) and 360 nm (Ac···Br2···Ac). The 238 nm peak in Br2(g) is associated with Br2···Br2 complexes, corroborated by a theoretical peak at 240 nm. A single peak at 415 nm in Br2(g) diluted in air is attributed to Br2···N2 complexes, with a corresponding theoretical peak at 417 nm. Theoretical and experimental data align well, validating the methodology and highlighting the role of XBs and electronic transitions in modulating Br2 spectrophotometric properties.