1H NMR study of isomerization in chlorotin(IV) ternary complexes of 8-quinolinol and 5,7-dichloro-8-quinolinol

A complete analysis of the temperature dependence (?30 to 52°C) of the ¹H NMR spectra in d-chloroform of the ternary complexes, bis-(8-quinolinato)tin(IV) dichloride and bis-(5,7-dichloro-8-quinolinato)tin(IV) dichloride has been performed. The intramolecular character of the exchange process has been established, and the spectra have been analyzed by the total lineshape method in terms of the interconversion of two isomers, the cis-cis-trans and the cis-trans-cis (with respect to Cl, N and O atoms), including the tin-proton couplings in the simulations. Arrhenius parameters of the process were E_a = 54 ± 1 and 52 + 1 kJ mol^?1, and log A = 11.8 ± 0.2 and 11.7 ± 0.3, respectively, for the two complexes. The similarity of the activation parameters obtained for both complexes indicates that the presence of bulky Cl atoms in the 8-quinolinol ring had no appreciable energetic influence on the isomerization process. Data were compared with those reported for other chlorinated hexacoordinated complexes, involving ligands other than the 8-quinolinol ring.