Synthetic and solution studies on metal complexes of N,N,N′,N′-tetrakis(2-carbamoylethyl)ethylenediamine

Abstract

The preparation of the tetra-amide ligand N,N,N′,N′-tetrakis(2-carbamoylethyl)ethylenediamine (H₂L) by Michael addition of ethylenediamine to acrylamide is described. The ligand forms complexes with Cu^II, Ni^II, Co^II, Fe^II, Mn^II, Ba^II, Zn^II, Cd^II, Hg^II, and La^III, which have been characterised in the solid state. With Cu^II, Ni^II, and Pd^II, deprotonated complexes [ML] can be prepared in solution and the solid state. For the other metal ions the complexes can be formulated as Mⁿ⁺(H₂L)Cl_n·xH₂O. The stepwise protonation of the ligand has been studied by potentiometric titration, giving log K₁= 7.20(1) and log K₂= 3.25(2) at 25 °C and I= 0.1 mol dm^–3(NaClO₄). Titration data for the molar ratio H₂L/M^II= 1 : 1 (M^II= Cu^II, Ni^II, or Pd^II) can be fitted to the stepwise equilibria (i)–(iii) and the corresponding log β values are reported. M²⁺+ H₂L [graphic omitted] [M(H₂L)]²⁺(i), M²⁺+ H₂L [graphic omitted] [M(HL)]⁺+ H⁺(ii), M²⁺+ H₂L [graphic omitted] [ML]+ 2H⁺(iii)