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.