Density Functional Theory Calculations of Vibrational Circular Dichroism in Transition Metal Complexes:  Identification of Solution Conformations and Mode of Chloride Ion Association for (+)-Tris(ethylenediaminato)cobalt(III)

Abstract

Density functional theory calculations of the vibrational circular dichroism (VCD) spectra of a transition metal complex, (+)-tris(ethylenediaminato)cobalt(III) as a free ion and with associated chloride ions, are reported. By comparison with experimental data obtained in our laboratory in 1986 (Young et al. J. Am. Chem. Soc. 1986, 108, 7255) and new measurements, this study identifies, for the first time, the geometry and absolute configuration of the association complex as Λ-δδδ-Co(en)3Cl2 +, in which two chloride ions each associate with three NH bonds along the C 3-axis of a D 3-symmetry complex. The DFT calculations, carried out with both the LanL2DZ and 6-31G(d)[C, H, N]/Stuttgart ECP [Co] basis sets, predict the energy order of ethylenediamine ring conformations as λλλ < λλδ < λδδ < δδδ for the free (gas phase) Λ-Co(en)3 3+ ion, an order opposite to that deduced from solution studies. The VCD studies identify the δ-conformation as the most prevalent in solution for halide and sulfate counterions, suggesting an interaction with solvent or weakly associated counterions that stabilizes this conformation.

A vibrational circular dichroism implementation within a Slater-type-orbital based density functional framework and its application to hexa- and hepta-helicenes

“…We have thus demonstrated that our implementation is correct and therefore can be applied for theoretical predictions of VCD spectra, which, as already shown [32,33,37,[41][42][43][44][45], is an important pre-requisite for interpretations of complicated experimental spectra of larger molecules, the assignment of absolute configurations of chiral substances, and the detection of specific interactions in chiral super-molecular aggregates, which manifest themselves in molecular vibrations.…”

Vibrational and electronic circular dichroism of Δ-TRISPHAT [tris(tetrachlorobenzenediolato)phosphate(V)] anion

“…To our knowledge, experimental and theoretical studies on D 3 -symmetric molecules, however, have been limited. 62 This prompted us to study the VCD spectrum of the ammonium TRISPHAT salt both experimentally and theoretically. Figure 4 shows the optimized structure of the isolated TRISPHAT anion.…”

Absolute configuration determination of chiral molecules in the solution state using vibrational circular dichroism

“…Recent publications include stereochemical analyses of a chiral oxathiane, 79 a chiral 1,4-oxazin-2-one, 80 a vasopressin receptor antagonist, 81 mirtazepine, 82 and (R)-(+)-1-(9-phenanthryl)ethylamine. 83 From our laboratory at Syracuse University, the first VCD calculations on transition metal complexes, (+)-tris(ethylenediaminato)cobalt(III) 41 and Zn sparteine complexes have been published recently. 42 Some of these and other applications are highlighted in more detail below.…”