Metal Complexes Containing Six-Membered Chelate Rings. I. Preparation and Structure of 2,4-Pentanediaminetetraacetato Complexes of Cobalt(III)

New cobalt(III) complexes with 2,4-pentanediaminetetraacetate (2,4-ptnta4−) have been prepared. The optically active 2,4-ptnta4− (RR or SS) forms a sexadentate complex and determines the absolute configuration around the metal ion. The meso-2,4-ptnta4− (RS) coordinates to the metal ion as a quinquedentate with a free acetate branch. Such stereospecific formations of sexa- and quinquedentate complexes from the optically active and the meso 2,4-ptnta4− have been attributed to the steric regulation coming from the methyl groups on the α-carbon atoms.