Nickel(II) Complexes of N‐Alkyl‐Substituted Diamino Diamides in Aqueous Solution

In order to study the steric, inductive, and ring‐strain effects of diamino diamides on the equilibrium and spectral properties of nickel(II)‐diamino diamides complexes, four tetradentate ligands, 4‐methyl‐4,7‐diazadecanediamide(4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide(4,7‐N,N'‐Me2‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐L‐2,2,2), and 4‐methyl‐4,8‐diazaundecanediamide (4‐Me‐L‐2,3,2), have been synthesized. Their protonation constants have been determined potentiometrically in 0.1M KCl at 25.0°C The formation of their nickel(II)‐complexes and the Ni‐O to Ni‐N bond rearrangements at the two amide sites of these complexes have been investigated quantitatively by potentiometric and spectrophotometric techniques under the same conditions. Electronic spectra of the nickel(II)‐complexes of these ligands and their deprotonated species formed in aqueous solution were measured and discussed.