ELECTRONIC-STRUCTURE OF THE COENZYME VITAMIN-B-12 AND RELATED SYSTEMSPART II - A CORRIN MODEL SYSTEM

We present a theoretical study of the geometric structure of Co(corrin )(L)(R)(+) (R = CH3, i-C3H7 and adenosyl and L = NH3, pyridine and 5,6 -dimethylbenzimidazole) as model systems for the vitamin B-12 coenzyme . We have optimized the geometries of nine corrin derivatives with axi al ligands of varying degrees of steric bulkiness. In addition, we hav e included reoptimized geometries for nine dimethylglyoxime derivative s. Our goal was to compare and contrast calculated geometries for corr in models to those found for the corresponding dimethylglyoxime deriva tives, which are often used as a model of the corrin group in experime ntal systems. We found that the dimethylglyoxime model is appropriate for axial Co-C distances, but not for axial Co-N distances. (C) 1998 E lsevier Science B.V.