Synthesis and characterization of hexadentate cobalt(III) complexes with novel edta-type ligands Part 2. Circular dichroism of the trans(O 5O 6) and trans(O 6) isomers of a cobalt(III) complex of 1,3-propanediamine- N,N′-diacetic- N,N′-di-3-propionic acid

Abstract

Cobalt(III) complexes with the hexadentate ligand, 1,3-propanediamine- N,N′-diacetate- N,N′-di-3-propionate ion (1,3-pddadp) were prepared, chromatographically separated into two geometrical isomers with respect to the NO chelate ring size [ trans(O 5O 6) and trans(O 6)], and resolved. The 1H NMR, electronic absorption and circular dichroism (CD) spectra were used to characterize the complexes. The splitting of the T 1g( O h ) band of the trans(O 6-[Co(1,3-pddadp)] − complex indicates that the tetragonal field is enhanced, relative to the fields in other [Co(edta)] − -type complexes reported. The (+) 546- trans(O 5O 6)-[Co(1,3-pddadp)] − and (+) 546- trans(O 6)-[Co(1,3- pddadp)] − complexes with a positive CD peak at lowest energy in the first spin-allowed d-d absorption band region are tentatively assigned the Λ absolute configuration. Preliminary results of a crystallographic study of the K trans(O 6)-[Co(1,3-pddadp)]·3H 2O confirm the assignments of geometrical isomers of the complexes.