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 ⁴E_g 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 ⁴E_g state of the corresponding low-spin species.