F. Bouchard, V. Brenner, C. Carra, W. Hepburn, G. K. Koyanagi, T. B. McMahon,
G. Ohanessian, and M. Peschke

Department of Chemistry, UniVersity of Waterloo, Waterloo, Ontario, Canada N2L 3G1, Département de
Chimie, Laboratoire des Méchanismes Réactionnels (URA 1307 CNRS), Ecole Polytechnique,
91128 Palaiseau Cedex, France, Institute de Chimie Physique, UniVersitéde Fribourg, Perolles,
Fribourg CH-1700, Switzerland, and Laboratoire de Chimie Theorique, DSM/DRECAM/SPAM,
CE-CEA Saclay, 91191 Gif-sur-YVette, France

Received: January 28, 1997; In Final Form: June 6, 1997

Abstract: A new experimental apparatus is described which permits the determination of binding energetics for metal-
ligand complexes. This technique mates laser ablation for the generation of atomic metal ions with the
environment of a high-pressure ion source which leads to rapid termolecular stabilization of metal ion-ligand
complexes containing one or more ligands. The time resolved capability of the detection system allows
equilibrium to be studied quantitatively for binding energies in the range of 5-30 kcal mol^-1 . Such
measurements of the absolute binding energy of formaldehyde to Al⁺ combined with existing bimolecular
Al⁺ exchange equilibrium data leads to an absolute Al⁺ affinity scale. For two ligand complexes an extensive
ab initio search of the potential energy surfaces shows that the experimentally observed species involving
CH₃CN and (CH₃)₂O involve simple ligand complexation with an acute L-Al-L bond angle (L = ligand)
rather than hydrogen bonded or inserted structures. In one instance a third ligand complexation has been
experimentally investigated likely leading to a species of pyramidal geometry.