Nickel complexes of N-substituted iminodiacetates in aqueous solution: co-ordination by the hydroxyl group of hydroxyalkyl substituents

Abstract

Nickel(II) complexes of substituted iminodiacetates, RN(CH₂CO₂^–)₂, have been studied in aqueous solution [R = Et, Prⁿ. Prⁱ, Buⁿ, Buⁱ,Bu^s, Bu^t, n- and t-pentyl, HOCH₂CH₂, HOCHMeCH₂, HOCH₂CHMe, HOCMe₂CH₂, HOCH₂CMe₂, HO(CH₂)₃, HO(CH₂)₄, and HO(CH₂)₅]. Stability constants have been determined for the 1 : 1 and 1 : 2 complexes; comparisons among the values found support earlier suggestions that the substituent hydroxyl group is co-ordinated only in the 1 : 1 complexes with the HO(CH₂)₃, ligand and with all the hydroxyethyl ligands. The proton resonance spectra of the complexes confirm these suggestions. At < 0 °C, the complex with R = HO(CH₂)₃ shows a spectrum typical of a rigid puckered conformation for the six-membered chelate ring formed by this substituent group. Electronic spectra and magnetic moments have also been determined for the complexes: they are consistent with approximately octahedral co-ordination around the nickel.