Spectrophotometric study of formation, structure, stability and kinetics of charge-transfer complexation of iodine with 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane in chloroform solution. Application of hard-modeling approaches and theoretical calculations

Abstract

Interaction of 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane (HMHA18C6) with iodine was investigated spectrophotometrically in chloroform solution using hard modeling approaches. The observed time dependence of the charge-transfer band and subsequent formation of I3- in solution were indicative of the slow transformation of the initially formed 1:1 HMHA18C6.I2 outer complex to an inner electron donor–acceptor (EDA) complex (HMHA18C6.I+)I−, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first order rate constants for the transformation process at various temperatures, calculated from the corresponding absorbance-time data, were used to obtaining the activation parameters Ea, ΔH#, and ΔS# for process. The formation constant and concentration- and spectral profiles of the resulting electron EDA complex have also been obtained by applying multivariate nonlinear least squares hard-modeling approach on the collected experimental data matrix. Small values of sum of squares of the residuals (ssq) obtained showed the proper selection of the model. The optimized structures of HMHA18C6 and its (HMHA18C6-I+)I3- complex were also calculated at DFT-B3LYP level using 6-31G* basis set and discussed in the text.