Theoretical analysis of the individual contributions of chiral arrays to the chiroptical properties of tris-diamine ruthenium chelates.

Calculations of the excitation energies, oscillator and rotational strengths, and the CD spectra of 16 diastereoisomers of the tris-diamine ruthenium chelates Ru(en)(3), Ru(pn)(3), and Ru(bn)(3) have been performed at the TDDFT/B3LYP/LanL2DZ+6-31G* level including solvent effects. The individual contributions of the chiral arrays, Delta/Lambda octahedral core, delta/lambda twists of the ligand rings, and R/S chiral carbons to the rotational strengths of related transitions have been quantitatively determined and graphically presented. It was found that the three chiral arrays Delta, delta and S each make their contributions to the CD spectra of the chelates with the sign alternated between negative and positive from long wavelength to short, but the intensities of the extrema are different for different chiral arrays. By simply combining the contributions of related chiral arrays in the chelates, all CD spectra of the 16 isomers obtained at the TDDFT level can be well reproduced, and those of the other conformers can also be well predicted, as expected. These findings not only make it possible to determine the absolute configurations and conformations of related chelates in solution from their CD spectra but also provide a deep insight into the chiroptical properties of the chelates.