Polyamine ligands. II. Nickel(II) complexes with the tridentate ligand 5-(2'-Pyridyl)-3-azapentan-1-amine

Abstract

The tridentate amine 5-(2'-pyridyl)-3-azapentane-1-amine (pap) forms a series of stable nickel(II) complexes of the composition Ni(pap)X2 (X = Cl, Br, I, NO3, SCN, ½SO4) and [Ni(pap)2]X2 (X = ClO4, I). Measurements of their electronic absorption spectra, infrared spectra, molar conductance, and magnetic susceptibility indicate that the complexes contain the amine coordinating as a tridentate ligand. In general, the Ni(pap)X2 compounds appear to possess a tetragonally distorted, octahedral structure with bridging anions in the solid state and a solvated complex structure in solution. The [Ni(pap)z]X2 compounds contain two tridentate ligands coordinated to one nickel ion, forming the octahedral NiN6 structure. Geometrical isomerism has been observed in the [Ni(pap)2]I2 compound which can be isolated as a yellow or a pink modification; this isomerism has been attributed to the alternative modes of coordination by the tridentate ligand. The isomerization of the unstable yellow form to the more stable pink form has been followed spectrophotometrically at 28° and appears to be first order in concentration.