Shape-conserving enhancement of vibrational circular dichroism in lanthanide complexes

Abstract

The VCD spectra of lanthanide chelates with two chiral ligands display conserved sequences of bands throughout the Ln series. Some compounds (Tm, Yb) feature increased bands and strongly improved signal-to-noise ratios, an effect we dub Lanthanide Induced VCD Enhancement (LIVE).

Lanthanide Tris(β‐diketonates) as Useful Probes for Chirality Determination of Biological Amino Alcohols in Vibrational Circular Dichroism: Ligand to Ligand Chirality Transfer in Lanthanide Coordination Sphere

“…S2 and S3). 22 and is similar to that observed in induced ECD intensity of probe 1a-1g with 6c. 40 Since their ionic radii increased on the order Yb 3+ (0.99 Å) < Er 3+ (1.00 Å) < Ho 3+ (1.02 Å) < Dy 3+ (1.03 Å) < Gd 3+ (1.05 Å) < Eu 3+ (1.07 Å) < Pr 3+ (1.13 Å) for octadentate coordination, 34 it is likely that steric proximity between the coordinating β-diketonates and the chiral center of the amino alcohol 6c regulates the chirality transfer in the lanthanide coordination sphere.…”

“…The order of influence of various ligands was 1 > 3 > > 2 , 4 . Interestingly, the order for various lanthanide centers was Yb(III) ~ Er(III) ~ Ho(III) > Dy(III) ~ Gd(III) ~ Eu(III) >> Pr(III), which has no correlation with the order of the lanthanide‐induced VCD enhancement reported by the group of Di Bari (Tm 3+ >> Yb 3+ ~ Tb 3+ > Nd 3+ ~ Pr 3+ for chiral cyclen and Tm 3+ > Tb 3+ > Yb 3+ > Dy 3+ > Ho 3+ ~ Er 3+ for lasalocid) and is similar to that observed in induced ECD intensity of probe 1a , 1b , 1c , 1d , 1e , 1f , 1g with 6c . Since their ionic radii increased on the order Yb 3+ (0.99 Å) < Er 3+ (1.00 Å) < Ho 3+ (1.02 Å) < Dy 3+ (1.03 Å) < Gd 3+ (1.05 Å) < Eu 3+ (1.07 Å) < Pr 3+ (1.13 Å) for octadentate coordination, it is likely that steric proximity between the coordinating β‐diketonates and the chiral center of the amino alcohol 6c regulates the chirality transfer in the lanthanide coordination sphere.…”

“…13 Another advantage of the VCD method is that the observed VCD spectral information can be successfully combined with theoretical calculations for practical analyses of organic molecules, [13][14][15][16][17] and VCD was recently applied in the characterization of chiral metal complexes. [18][19][20][21][22][23][24][25] Although the chirality determination of a chiral molecule with IR-inactivity or small activity requires complexation with IR-active probe in the VCD method, this kind of example has rarely been reported.…”

Comparison of the Electronic and Vibrational Optical Activity of a Europium(III) Complex

“…A study on Cs I ion‐containing Ln III complexes linked the VCD intensities with the parity of the total orbital angular momentum ( L ) 23. Lanthanide ions also sometimes cause an enhancement of the VCD intensities, whereas the positions and relative magnitudes of the bands are conserved 24. In the case of the bipyridine complex described in the present study, however, we observe both VCD enhancement and intensity distortion.…”

Recent Trends in Chiroptical Spectroscopy: Theory and Applications of Vibrational Circular Dichroism and Raman Optical Activity

“…Unusually large VCD is also often observed for transition metal complexes, containing Co 2+ , Co 3+ , Ni 2+ , and other coordinating ions . Clearly, this effect must be different than for the condensation‐induced enhancement observed for the nucleic acids, fibrils and crystals.…”