Density Functional Calculation of the Electronic Circular Dichroism Spectra of the Transition Metal Complexes [M(phen)₃]²⁺(M = Fe, Ru, Os)

Abstract

The circular dichroism spectra of the tris-bidentate metal complexes Lambda-[M(phen)3]2+, with M = Fe, Ru, Os and phen = 1,10-tris-phenanthroline, are investigated computationally, employing time-dependent density functional theory. Good agreement with experimental spectra is obtained for Ru and Os. The Lambda-[Os(phen)3]2+ spectrum is analyzed in detail. It is shown how relativistic effects red shift CD bands where the Os 5d-orbital participates to a large extent in the excitations. Further, the participation of the metal in the ligand pi --> pi exciton CD is determined to be of the order of 10%. Though solvent effects can have a noticeable effect on individual transitions and rotatory strengths, they are demonstrated to have only a very small overall effect on the resulting simulated CD spectra. For Lambda-[Fe(phen)3]2+, the results are shown to be rather sensitive to the choice of the applied hybrid and nonhybrid density functionals, and the optimized geometries based thereupon. In particular, the sign pattern of the lower-energy part (up to 33 x 10(3) cm(-1)) of the Lambda-[Fe(phen)3]2+ CD spectrum is difficult to reproduce. Some combinations of functionals and geometries yield good agreement with experiment, but no "best" approach can be devised based on the available results. Possible sources of errors in the spectrum of Lambda-[Fe(phen)3]2+ due to deficiencies in the functionals and the exchange-correlation kernels are investigated.

On the origin of circular dichroism in trigonal dihedral d6 complexes of bidentate ligands containing only σ‐orbitals. A qualitative model based on a density functional theory study of Λ‐[Co(en)3]3+

“…[21][22][23][24] TD-DFT has proved to be an especially attractive approach as it gives reasonable accuracy at a low computational cost. Exploratory studies on the optical activity in tris-bidentate Co (III) and Rh (III) [21][22][23] complexes as well as other transition metal systems 24 have already appeared.…”

In Situ Assembly of Octahedral Fe(II) Complexes for the Enantiomeric Excess Determination of Chiral Amines Using Circular Dichroism Spectroscopy

“…The methods were based on recent literature reports on related Fe(II) complexes. 44–46 The results of geometry optimizations are shown in Table S1 (Supporting Information). The relevant geometries are shown in Figure 8.…”

Spectroscopic Properties Obtained from Time‐Dependent Density Functional Theory (TD‐DFT)

“…57,124,125 Likewise, problems with excitations involving metal d orbitals were noted for the -[Fe(phen) 3 ] 2+ complex, but not for the Ru and Os analogs. 123 Overall, the agreement with experiment can be considered satisfactory for the Co complex (and similar for other chiral complexes 124,125 ) and excellent for the Os complex. For the +3 charged Co complex, effects of inclusion of solvent is important, whereas they do not have much of an impact on -[Os(phen) 3 ] 2+ and its Fe, Ru analogs.…”

“…57,122 TD-DFT was previously found to reproduce the excitation spectra of a number of chiral Ru complexes quite well, 75 but no CD computations had been carried out. TD-DFT computations of the CD spectra of several tris-bidentate Co III complexes (including [Co(en) 3 ] 3+ ) as well as -[Rh(en) 3 ] 3+ were reported by Autschbach et al 57 The series [M(phen) 3 ] 2+ with M = Fe, Ru, Os was studied by Le Guennic et al 123 Two representative simulated spectra from Autschbach et al 57 and Le Guennic et al 123 are shown in Figure 3 in direct comparison with experiment. Le Guennic et al 123 also investigated the bipy 3 series (unpublished) during the course of the same study and found that the CD spectra were in similar agreement with experiment as those for the phen 3 systems.…”