A strong-field non-conjugated polyamine ligand: low-spin iron(II) and high-spin nickel(II) complexes

Abstract

Iron(II) and nickel(II) complexes of two new terdendate polyamines, di-(2-pyridylmethyl)amine (DPMA) and di (2-pyridylmethyl) methylamine (MeDPMA) are described. It is shown from analytical, electrical conductance, and spectral measurements that all the compounds contain the complex ion [M (ligand)₂]²⁺. The iron(II) compounds of DPMA have magnetic moments less than 0·8 B.M. and are the first examples of low-spin iron(II)–polyamine complexes in which there is no conjugation within the chelate ring. In contrast, MeDPMA forms high-spin iron(II) compounds. The strong-field nature of DPMA is confirmed by the high value (1255 cm.^–1) for Dq in [Ni(DPMA)₂]²⁺. The properties of the new complexes are compared with those of ligands containing the α-di-mine group and are discussed in relation to steric effects and to metal–ligand π-bonding.