Signatures of counter-ion association and hydrogen bonding in vibrational circular dichroism spectra

We study the effect of counter-ion complexation on the example of Cl(-) ions interacting with the [Co(en)(3)](3+) complex. The H-bonding of the N-H groups of the ethylenediamine (en) ligands with the Cl(-) ions may lead to giant enhancement of the VCD intensity for the N-H stretches, but may also le...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2011-01, Vol.13 (19), p.8811-8825
Main Authors: NICU, Valentin Paul, HESHMAT, Mojgan, JAN BAERENDS, Evert
Format: Article
Language:English
Subjects:
Chemistry
Complexation
Exact sciences and technology
Fingers
General and physical chemistry
Hydrogen bonding
Ligands
Mathematical analysis
Signatures
Spectra
Twisting
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Summary:We study the effect of counter-ion complexation on the example of Cl(-) ions interacting with the [Co(en)(3)](3+) complex. The H-bonding of the N-H groups of the ethylenediamine (en) ligands with the Cl(-) ions may lead to giant enhancement of the VCD intensity for the N-H stretches, but may also lead to VCD sign changes in the finger print region of N-H wagging, twisting and scissoring motions. Such sign changes should not be mistaken for signatures of the presence of the other enantiomer. We elucidate the mechanism for the sign changes and give a recommendation on how to deal with this problem. We also show that the experimental spectrum is only in good accord with the calculations if complexation of 5 Cl(-) ions (two axial, three equatorial) is assumed, but not with two (axial) or three (equatorial) Cl(-) ions, thus showing the potential of VCD to be used as an experimental probe for complexation.
ISSN:1463-9076
1463-9084
DOI:10.1039/c0cp02701d