Studies on the magnetic cross-over in five-co-ordinate complexes of iron(II), cobalt(II), and nickel(II). Part II

Abstract

The new terdentate ligand 2,6-di(diphenylphosphinomethyl)pyridine forms a series of crystalline complexes, MLX₂, with iron(II), cobalt(II), and nickel(II) halides and thiocyanates. Distorted square pyramidal structures are suggested on the evidence of their electronic spectra and other physical properties. Magnetic susceptibility measurements as a function of temperature classify the cobalt and nickel compounds as low-spin, high-spin, or as having an anomalous temperature-dependence. For the latter group a low-spin ⇌ high-spin equilibrium is suggested. All the iron complexes are fully high-spin over the temperature range studied. The suggested magnetic cross-over in these compounds is discussed in relation to that in previously reported compounds having a distorted trigonal bipyramidal structure.