Structure of expanded porphyrins : electron-nuclear multiple resonance and molecular orbital studies of texaphyrin anion radicals in solution

Abstract Liquid solution ENDOR and TRIPLE resonance experiments have been performed on texaphyrin radical anions generated by sodium reduction in tetrahydrofuran. Six proton and two nitrogen hyperfine couplings could be determined, including their signs. The results were compared with theoretical isotropic hyperfine couplings. They were calculated for energy-minimized texaphyrin structures, including the sodium metallo-derivative, by state-of-the-art SCF-MO methods (RHF-INDO/SP). This comparison suggests that in the course of the alkali metal reduction of texaphyrin the acidic hydrogen in the macrocycle is replaced by sodium.