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Accurate measurement of the relative bond energies of CO and H 2 O ligands in Fe + mono‐ and bis‐ligated complexes
Author(s) -
le Caër Sophie,
Heninger Michel,
Maître Philippe,
Mestdagh Hélène
Publication year - 2003
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.916
Subject(s) - chemistry , fourier transform ion cyclotron resonance , ligand (biochemistry) , mass spectrometry , analytical chemistry (journal) , equilibrium constant , ion cyclotron resonance , ion , cyclotron , organic chemistry , biochemistry , receptor , chromatography
The systems Fe(H 2 O) n + /COH 2 O and Fe(CO) n + /COH 2 O (n = 1 and 2) were investigated in a triple cell Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. Using mixtures of CO with a very small amount of water, the ligand exchange equilibrium was reached, allowing experimental determination of the relevant equilibrium constants and free energies of reaction. Quantum chemical calculations at the B3LYP level of theory on the reactant and product species allowed us to determine the entropic terms and to derive the relative bond energies of CO and H 2 O in the mono‐ and bis‐ligated complexes. For n = 1, H 2 O is more strongly bound to Fe + than CO by 4.1 ± 1.6 kJ·mol −1 at 298 K. For n = 2, at the same temperature, H 2 O is more strongly bound than CO to (H 2 O)Fe + by 7.6 ± 1.6 kJ·mol −1 , and to (CO)Fe + by more than 20.1 kJ·mol −1 . Copyright © 2003 John Wiley & Sons, Ltd.