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-diazadecanediam ide-(4-Me-L-2.2,2), 4.7-dimethyl-4,7-diazadecanediamide (4,7-N,N'-Me-2-L-2, 2,2,), 4-ethyl-4,7-diazadecane-diamide (4-Et-L-2,2,2), and 4-methyl-4,8-dia zaundecanediamide (4-Me-L-2,3,2), have been synthesized. Their protonation constants have been determined potentiometrically in 0.1M KCl at 25.0 degre es 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 investig ated quantitatively by potentiometric and spectrophotometric techniques und er the same conditions. Electronic spectra of the nickel(II)-complexes of t hese ligands and their deprotonated species formed in aqueous solution were measured and discussed.