Carbon-13 nuclear magnetic resonance study of the complexes formed between zinc(II) and triethylenetetramine

Abstract

The ¹³C n.m.r. spectra are reported as a function of pH for triethylenetetramine (then) and mixtures of trien and zinc nitrate. At decimolar concentrations the complexes formed are all substitution labile on the n.m.r. time-scale, but separate signals from free and complexed ligand were obtained at millimolar concentrations and low pH. The pH profiles for the exchanging systems have been analysed by computer and the chemical shifts of the three non-equivalent carbon atoms determined for the following species: trien, Htrien⁺, H₂trien²⁺, H₃trien³⁺, H₄trien⁴⁺, [Zn(trien)(OH₂)]²⁺, [Zn(Htrien)]³⁺, [Zn(trien)₂]²⁺, [Zn(trien)(Htrien)]³⁺, and [Zn(trien)(OH)]⁺. The stability constants of [Zn(Htrien)]³⁺, [Zn(trien)₂]²⁺, and [Zn(trien)(Htrien)]³⁺ have also been determined.