Synthesis, protonation and Cu2+ co-ordination studies on a new family of thiophenophane receptors

The synthesis of the new thiophenophanes 2,5,8,11-tetraaza[12](2,5)thiophenophane (L-1), 2,6,9,13-tetraaza[14](2,5)thiophenophane (L-2) and 2,5,8,11,14-pentaaza[15](2,5)thiophenophane (L-3) is described. The stepwise protonation constants of the macrocycles are determined by pH-metric titration and their protonation patterns are analysed by means of H-1 and C-13 NMR spectroscopy. L-1 and L-2 present first protonation on the thenylic nitrogens while L-3 protonates first on the central nitrogens of the polyamine bridge. Molecular orbital calculations are used to locate the atomic orbitals contributing to the HOMO of the free amines; The interaction with Cu2+ shows for L-1 and L-3 formation of binuclear complexes which readily hydrolyse to give very stable species, Electrochemical studies show for all three Cu2+-receptor systems an important stabilisation of the Cu+ oxidation state towards its disproportionation into Cu2+ and Cu-0 oxidation states.