Conformational analysis of coordination compounds. IV. Conformational energies and activation energies for ring inversion of ethylenediamine complexes

Autor:	James K. Beattie, Clifford J. Hawkins, J. R. Gollogly
Rok vydání:	1971
Předmět:	chemistry.chemical_classification Ring flip Chemistry Metal ions in aqueous solution Ethylenediamine Spectral line Coordination complex Inorganic Chemistry Bond length NMR spectra database chemistry.chemical_compound Crystallography Physical and Theoretical Chemistry Methylene
Zdroj:	Inorganic Chemistry. 10:317-323
ISSN:	1520-510X 0020-1669
DOI:	10.1021/ic50096a020
Popis:	The free energy differences between the various configurations of M(en) have been calculated for a number of M-N bond lengths. The marked preference for configurations of the types d(δδδ), L(λλλ), d(δδλ), and L(λλδ) which occuss for M-N = 2.0 A was found largely to be removed for complexes with M-N = 2.3 A. The calculations included for the first time an estimation of an entropy contribution to the conformational energies arising from differences in the vibrational freedom of the chelate rings in the various configurations. The calculations also included a study of the lowest energy transition state for ring inversion. This was found to be of the envelope type and to provide a barrier to inversion of about 5 kcal mol for M-N = 2.0 A increasing to about 7 kcal mol for M-N = 2.3 A. The results of the calculations weee used as the basis for a rationalization of the observed nmr spectra of the tris-ethylenediamine complexes of a number of metal ions. It was concluded that the room-temperature spectra weee the result of rapid ring inversion, the variation with the metal ion being due to a number of factors controlling the effective chemical shift difference between the axial and equatorial methylene protons.
Databáze:	OpenAIRE
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