UV-Visible spectroscopy and density functional study of solvent effect on halogen bonded charge-transfer complex of 2-Chloropyridine and iodine monochloride

Abstract

2-Chloropyridine and Iodine monochloride form 1:1 n → σ∗ charge transfer complex which is confirmed by Benesi Hildebrand plot using UV-vis spectroscopy. Multiple Linear Regression Technique (MLRT) shows that 2-Chloropyridine-ICl complex is susceptible to medium effect in reference to different solvent parameters, at both the bulk and molecular levels. Dielectric constant (∈), refractive index (n), Hansen parameter, Catalan parameter and Kamlet’s π∗ values give good linear fit equations between experimental and calculated CT bands with R2 values as high as 1. Polarizability effect on the CT band is examined using Buckingham and Lippert Mataga equation. Formation constant of the complex in different mediais found to be linearly dependent on Hansen solubility parameter. Computational analysis defends well the blue shift in polar medium observed for 2-Chloropyridine-ICl. NBO, NRT, and QTAIM analyses explain a shift from ionic character to covalent character in polar medium. It emphasises a stronger donor acceptor interaction in polar medium and thereby explains the experimentally observed blue shift. A logarithmic relation between the bond lengths of the bridging atoms and dielectric constant is proposed. Keywords: MLRT, Solvent parameter, NBO, NRT, QTAIM