Complexes formed between zinc(II) and diethylenetriamine: a carbon-13 nuclear magnetic resonance study

Abstract

Carbon-13 n.m.r. spectra are reported as a function of pH for mixtures of diethylenetriamine (dien) and zinc nitrate, and of zinc and dien with 1,2-diaminoethane (en), 1,3-diaminopropane (pn), acetate, glycine (gly), and L-alanine (ala). Carbon-13-chemical shifts are also reported as a function of pH for dien and gly (carboxylate carbon) alone. The pH profiles have been analysed by computer and the chemical shifts of the methyl, methylene, methine, and carboxylate carbon atoms determined for the following species: dien, Hdien⁺, H₂dien²⁺, H₃dien³⁺, [Zn(dien)]²⁺, [Zn(dien)(Hdien)]³⁺, [Zn(dien)₂]²⁺, [Zn(dien)(en)]²⁺, [Zn(dien)(pn)]²⁺, [Zn(dien)(MeCO₂)]⁺, [Zn(dien)(glyO)]⁺, [Zn(dien)(alaO)]⁺, [Zn(Hdien)₂(en)]⁴⁺, [Zn( Hdien)₂(pn)]⁴⁺, [Zn( Hdien)₂-(glyO)]³⁺, [Zn(Hdien)₂(alaO)]³⁺. Stability constants have also been determined for the bis and ternary complexes. [Zn(dien)(OH)]⁺ does not appear to be formed to any significant extent. Potentiometric titrations with dien and zinc + dien solutions provide support for the interpretation of the chemical-shift data. The implications of the results as to the co-ordination geometry of zinc in these complexes are discussed.