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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Published inPhysical chemistry chemical physics : PCCP Vol. 13; no. 19; pp. 8811 - 8825
Main Authors NICU, Valentin Paul, HESHMAT, Mojgan, JAN BAERENDS, Evert
Format Journal Article
LanguageEnglish
Published Cambridge Royal Society of Chemistry 01.01.2011
Subjects
Chemistry
Complexation
Exact sciences and technology
Fingers
General and physical chemistry
Hydrogen bonding
Ligands
Mathematical analysis
Signatures
Spectra
Twisting
Vibrational transition
Complexation
Motion
Association
Enantiomer
Counter ion
Calculation
Potential
Complexes
Mechanism
Circular dichroism
Hydrogen bond
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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.
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ISSN:1463-9076
1463-9084
DOI:10.1039/c0cp02701d