Stoichiometry, thermodynamics and kinetics of host-guest interactions between cryptand C222 and iodine in 1,2-dichloroethane. Formation of a C222.I+ inclusion cryptate

The host-guest molecular complexation reaction between cryptand C222 and io dine has been studied spectrophotometrically in 1,2-dichloroethane solution . The resulting 1 : 1 and 2 : 1 (I-2 to C222) complexes were formulated as (C222 ... I+)I- and (C222 ... I+)I-3(-), respectively. The enthalpy and ent ropy of the complex formation reactions were evaluated from the temperature dependence of the formation constants. The resulting complexes are both en thalpy and entropy stabilized. The spectrophotometric, NMR, conductometric and potentiometric results emphasize that the complexes are positive iodine cryptates. The rate constants for the formation and proton-assisted dissoc iation of the (C222 ... I+)I-3(-) complex at various temperatures and the c orresponding activation parameters were evaluated. Based on the results thu s obtained, possible pathways for the complexation reaction are proposed.