Thermodynamic, NMR and photochemical study on the acid–base behaviour of N,N′-dibenzylated polyamines and on their interaction with hexacyanocobaltate(III)

Abstract

The synthesis and protonation behaviour of the dibenzylated open-chain ligands 1,4-dibenzyl-1,4-diazabutane (L¹), 1,7-dibenzyl-1,4,7-triazaheptane (L²), 1,10-dibenzyl-1,4,7,10-tetraazadecane (L³), 1,12-dibenzyl-1,5,8,12-tetraazadodecane (L⁴) and 1,13-dibenzyl-1,4,7,10,13-pentaazatridecane (L⁵) are presented. The protonation behaviour has been studied by means of pH-metric measurements, NMR, absorption UV–VIS and steady-state fluorescence emission spectroscopy. The influence of the aromatic ring on the acid–base behaviour of these ligands is discussed. The association constants of these ligands with [Co(CN)₆]^3– have been calculated by steady-state fluorescence emission. The reduction in the quantum yield for the photoaquation reaction of [Co(CN)₆]^3– in the presence of L⁵ suggests that three out of the six cyanide groups of the anion are involved in the formation of the hydrogen-bond network of the supramolecular adduct.