Hydrogen-1 and carbon-13 nuclear magnetic resonance studies of nickel(II) complexes of uninegative quadridentate ligands derived from diamines and β-diketones

Abstract

The preparation is described of a series of diamagnetic nickel(II) complexes, (III), of open-chain quadridentate ligands derived from the condensation in situ, in a 2 : 1 molar ratio, of ethylenediamine or propylenediamine with a β-diketone. A comparative 1H and 13C n.m.r. study of these and other related complexes is presented; the structures are discussed in terms of the n.m.r. data. Complex (IIIg), derived from (RS)-propylenediamine and pentane-2,4-dione, is assigned a symmetrical structure (IV) in which methyl substituents are attached to the carbon atoms adjacent to the co-ordinated amine groups. The data also indicate that the complex exists as meso and rac isomers which arise from different relative orientations of the methyl substituents. The 13C n.m.r. data for the open-chain complexes derived from ethylenediamine, (IIIa)–(IIIe) and (IIIh), correlate well with similar data for a related macrocyclic ligand complex (II) in which the cyclic ligand is derived from 1 : 1 condensation of pentane-2,4-dione and 3,6-diazaoctane-1,8-diamine.