Accurate measurement of the relative bond energies of CO and H2O ligands in Fe+ mono- and bis-ligated complexes.
The systems Fe(H(2)O)(n) (+)/CO[bond]H(2)O and Fe(CO)(n) (+)/CO[bond]H(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 x 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 x mol(-1), and to (CO)Fe(+) by more than 20.1 kJ x mol(-1).
le Caër
Sophie
S
Laboratoire de Chimie Physique, UMR 8000, CNRS, Bât. 350, Université Paris-Sud, 91405 Orsay cedex, France. sophie.lecaer@lcp.u-psud.fr
Heninger
Michel
M
Maître
Philippe
P
Mestdagh
Hélène
H