Collect. Czech. Chem. Commun. 1990, 55, 1427-1434

The empirical conformational surface of the co(ethylenediamine) ring

František Pavelčík and Eva Luptáková

Department of Analytical Chemistry, Pharmaceutical Faculty, J. A. Komenský University, 832 32 Bratislava


The conformational surface of the Co(en) chelate ring was studied by the method of structural correlation. The reduction of dimensionality of the conformation problem was achieved by employing the pseudorotation concept. The empirical potential surface was obtained by statistical treatment of 743 independent conformations from the Cambridge Structural Database. The theoretical potential surface was obtained by molecular mechanics. The minimal-energy conformation is gauche with the Co atom on the two-fold axis. Conformational flexibility also includes an envelope conformation with the N atom bent out of the plane. The transition between the mirror-image symmetrical conformations can occur by a pseudorotation pathway and is accompanied by increased planarity of the ring. The transition state is an envelope conformation with an out-plane Co atom.