Meeting of Northwest‐German Chemistry Lecturers

Abstract

Using an opitical method according to Briegleb [3], we were able to prove the existence of a 1:l-complex KO2in aqueous solution. The stability constant of this weak complex can be estimated to be K'," = 1.0 I/mole. From solubility data [4] we calculated K2C5 " = 0.8 I/mole.The results show [51 that the yellow adducts are charge transfer complexes of the Mulliken type [6], in which the iodide ions act as donors and the SOzmolecules as acceptors. Infrared spectroscopic measurements in acetonitrile led to the same result [2]. It was possible to calculate the complete term diagram of the complex [5,7]: WN = AH = -1.68, W,J = -0.12, W1 = 77.68, WE = 82.16 kcal/mole. Although we failed to obtain any indication of an addition compound in the course of tensimetric analysis of a solution o f iodine in liquid SO2 at -61.5 "C [S], low-temperature spectra of this solution (yrZ= 7 . 7~ 10-5) did show a definite shift of the iodine bands towards the blue; this shift increases with decreasing temperature. The maximum value for the iodine band is 493.5 m p at -14.7"C, 490 m p at -41.8"C, and 482.5 m p at -73.5 "C. The bathochromic shift of the iodine band is taken as definite evidence for the formation of a charge transfer complex according to the equation :The stoichiometric relationships of the complex are still unknown; its stability is low. Its enthalpy of formation at --15 'C is estimated [5] at AH = -2 kcal/mole and therefore corresponds to the stability of iodine/aromatic complexes. In this complex, the iodine molecule acts as donor, the SO2 molecule as acceptor. There are some other instances of this unusual donor function of the iodine molecule, viz. the autocomplex of iodine I4 [9] and the complex cation I3+ [lo].