VIBRATIONAL CIRCULAR DICHROISM IN TRANSITION METAL COMPLEXES. RING CONFORMATION AND RING CURRENTS
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Date
1986
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Ohio State University
Abstract
The vibrational circular dichroiam (VCD) spectra of tris complexes of Co(III) with ethylenediamine, $\beta$-alanine and $\alpha$-amino acid ligands have been investigated. Monosigante VCD features in the NH and CH stretching regione and CH bending region are attributed to magnetic dipole transition moments arising from oscillating electric current in the chelate ring or in rings closed by direct hydrogen bonding or anion bridging between ligands. The currents are generated by hydrogen stretchig or bending motion adjacent to or withing the rings. The analyses of the VCD spectra lead to qualitative and in some cases quantitative determination of the solutuion conformation of the five or six membered chelate rings. The VCD of the amino acid complexes is consistent with chelate rings which are puckered in such a way to permit the maximum exetent of $N-H\cdots o=c$ hydrogen bonding ($\sigma$ or $\pi$) between adjacent ligande. For the ethylenediamine complex, the addition of excess chloride ion resulte in a structure of $D_{3}$ symmetry with three $C_{1}^{-}$ bridges between $NH_{2}$ groups and all ethylenediamine rings in the lel conformation.
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Address: Department of Chemistry, Syracuse University. Syracuse. NY 13244-1200
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