New adducts of phthalocyaninatocobalt(II) with base molecules. Part 3. Chemical and spectroscopic relations between mono (low- and high-spin) and bis adducts

Abstract

New adducts of phthalocyaninatocobalt(II) with piperidine, 1-methylimidazole, 3,4-dimethylpyridine, 3,5-dimethylpyridine, 4-methylpyridine, 3-choloropyridine, pyrazine, 3-ethylpyridine, 4-ethylpyridine, 3-acetylpyridine, and 4-acetylpyridine have been synthesized. Strong σ-donor bases form bis adducts, while low σ ability favours the formation of mono adducts. All the bis adducts are low-spin species. Mono adducts may contain either low- or high-spin configurations. Apart from being favoured by the electronic properties of the base, the high-spin configuration is also favoured by steric hindrance and is probably accompanied by the exit of the cobalt atom out of the phthalocyaninato-plane. Electron spin resonance parameters provide evidence for the stabilization of the 4Eg state on passing from bis to mono adducts and for the removing of axial symmetry on passing from low-spin to high-spin mono adducts. It is suggested that the ground state of the high-spin mono adducts derives from the 4Eg state of the corresponding low-spin species.