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

Abstract
Time-dependent density functional theory (TD-DFT) is applied to the CD spectra of Λ(δδδ)-(+)-[Co(S-pn)n(en)3-n]3+ (n = 1, 2, 3) and Λ(δδδ)-(+)-[Co(en)3]3+ as well as the stereoisomers Δ-((δ)n(λ)3-n)-(−)-[Co(S-pn)n(en)3-n]3+ (n = 1, 2, 3) and Δ(δδδ)-(−)-[Co(en)3]3+. Theory is able to reproduce the major differences in the CD spectra of the species with a Λ-configuration and their isomers with a Δ-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 Λ-conformation compared to the Δ-configuration. Considerations were also given to the CD spectra of the lel3-isomer, Δ(λλλ)-(−)-[Rh(R-pn)3]3+ and the ob-isomer, Λ(λλλ)-(+)-[Rh(S-pn)3]3+.

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