On the origin of optical activity in tris-diamine complexes of Co(III) and Rh(III): A simple model based on time-dependent density function theory

Time-dependent density functional theory (TD-DFT) is applied to the CID spectra of (Co(S-pn)(n)(en)(3-n)](3+) (n = 1, 2, 3) and A(deltadeltadelta)-(+)-[Co(en)(3)](3+) as well as the stereoisomers Delta-((delta)(n)(lambda)(3-n))-Co(S-pn)(n)(en)(3-n)](3+) (n = 1, 2, 3) and A(deltadeltadelta)-(-)-[Co(en)(3)](3+). Theory is able to reproduce the major differences in the CD spectra of the species with a A-configuration and their isomers with a A-configuration in both the d-d and ligand-to-metal CT region. It is further possible to rationalize the trend in terms of a larger azimuthal distortion away from the octahedral geometry in the A-conformation compared to the Delta-configuration. Considerations were also given to the CD spectra of the /e/(3)-isomer, Delta( lambdalambdalambda)-(-)-(Rh- (R-pm)(3)](3+) and the ob-isomer, Delta(lambdalambdalambda)-(+)-[Rh(S-pn)(3)](3+).