Complexes of cobalt(II) halides with 4-methylpyridine and 2-methylpyridine

Abstract

Complexes of CoCl₂, CoBr₂, CoI₂, and Co(NCS)₂ with two and four molecules of 4-methylpyridine and two molecules of 2-methylpyridine have been prepared. Their magnetic properties, conductivities, and reflectance and absorption spectra in the visible region show that all the compounds of the type CoX₂B₂ are tetrahedral except Co(NCS)₂(4-mepy)₂, which is an octahedral polymer like its pyridine analogue. Infrared spectra in the 3-15 μ region lend no support to the suggestion that there may be differences in the extent of π-bonding between the metal and the base or the metal and NCS^- in tetrahedral and octahedral complexes. It is suggested that the position of the ligands in the spectrochemical series and the relative stabilities of the compounds CoX₂B₂ with respect to dissociation into CoX₂B₄ and free base can be explained in terms of repulsion effects between the non-bonding electron pairs on the ligands and metal d_є-orbitals on the one hand and the non-bonding electron pairs of neighbouring ligands on the other.