The preparations of the new amidine, N′-(2-pyridylmethyl)picolinamidine (ppa), and two methyl-substituted derivatives (Meppa and Me₂ppa) are described and their bischelate complexes with iron- and nickel-(II). Physical properties characterise the metal compounds as the hydrated salts of six-co-ordinate complex ions in which the ligands are terdentate, [M(ligand)₂]X₂,nH₂O (X = univalent anion). Magnetic and Mössbauer measurements show that the ppa complexes of iron(II) exist in a temperature-dependent high-spin ⇌ low-spin equilibrium in accordance with a prediction based on the ligand-field spectra of the nickel(II) complexes. The iron(II) complexes of the substituted ligands are fully high-spin over the temperature range investigated.

Electronic and Mössbauer spectra suggest that in the complexes the ligands are stabilised in the tautomeric form which provides for chelate ring conjugation, and that the local symmetry about the metal ion is approximately D_2d