Significance of the Orientation of Coordinated Imidazole and Benzimidazole Groups in Haemoprotein and Vitamin B12 Structures

Details of the structure of the dioxygen complex, Co(bzacen)(py)02 py = pyridine; bzacen = N,N'-ethylenebis(benzoylacetoniminide), PhC(O-)=CHC-(Me)=NCH2-)2, a possible model compound for oxygenated haemoproteins (RodIey and Robinson 1972), have prompted a study of the metal-ligand bonding in this compound and related biological systems. It has already been noted (RodIey and Robinson 1972) that the orientation of the benzimidazole group in the vitamin B12 structures resembles closely that found for the pyridine plane in Co(bzacen)(py)02 (Fig. 1), and the recently determined structure of ferricytochrome c (Dickerson et al.