CD Spectra and Absolute Configurations of fac(a,b,c)-[Co(a)(b)(c)(1,4,7-Triazacyclononane)]n+ Complexes

Seventeen kinds of fac(a,b,NH3)-[Co(a)(b)(NH3)(tacn)]n+ complexes (a, b=CN−, NO2−, SO32−, NCS−, N3−, CH3COO−, H2O, OH−, Cl−, or Br−; tacn=1,4,7-triazacyclononane) have been prepared and optically resolved by column chromatography. The absolute configurations of these complexes have been determined by referring to the CD spectra of the related [Co(a)(gly)(tacn)]n+ complexes (a=CN−, NO2−, NCS−, N3−, or Cl−). It has been found that the signs of the Cotton peaks observed in the first absorption band region are closely related to the ligand field strengths of the unidentate ligands, and that the dominant Cotton peak is associated with the electronic transition which arises in the plane containing no ammonia molecule.