Crystallographic Studies of Synthetic Corrinoids. III. Structural similarities and differences between A/D-seco-corrinoid complexes of divalent nickel,palladium and platinum

X-ray crystal structure investigations of the isomorphous perchlorate salts of complexes of an A/D-seco-corrinoid ligand (I) with divalent nickel, palladium and platinum are reported. The structures determined for the Pd- and Pt-complexes are virtually superposable, that of the Ni-complex, although similar to the other two, shows significant differences with respect to metal coordination and to the spatial relationship of the A and D rings and their substituents. These similarities and differences are discussed in relation to the photochemical A/D cyclization leading to corrin complexes (II).