Proton NMR spectra and structure of chlorotin(IV) ternary complexes of 8-quinolinol and its 5,7 dichloro and 2 methyl-5,7 dichloro derivatives

The low temperature ¹H NMR spectra in d-chloroform of the ternary complexes bis-(8-quinolinato) tin(IV) dichloride, bis-(5,7 dichloro-8-quinolinato) tin(IV) dichloride, and bis-(2 methyl-5,7-dichloro-8-quinolinato) tin(IV) dichloride have been obtained. The spectra showed that for the three complexes, only two configurations were appreciably populated, their free energy differences being equal to 0.28, 0.08 and ?0.04 kcal/mol respectively. The proton chemical shifts, the ¹H-¹H coupling constants and some of the ¹H-¹¹⁹Sn coupling constants have been obtained for each complex in the two configurations. An approximate computation of chemical shifts, including aromatic ring magnetic anisotropies and electric effects from polar groups, allowed the identification of the two configurations as the cis-cis-trans and the cis-trans-cis (with respect to Cl, N and O atoms), the former being the more populated one.