On the structure of Al(acetone) +2

Abstract

Initial results from direct clustering measurements of enthalpies and entropies of binding of acetone to Al + using a high pressure mass spectrometer led to the hypothesis that ligandligand bonding was involved in Al(acetone) + 2. In this study, however, collision-induced dissociation, ligand-displacement reactions, and infrared multiphoton photodissociation of the mixed species Al(acetone)(acetone- d 6) + in a Fourier transform mass spectrometer show that the two acetone ligands in Al(acetone) + 2 must be equivalent. Ab initio calculations support the conclusion that there are no ligandligand bonds, but that polarisation of the Al + leads to both acetones binding on the same side. The resulting ligandligand interaction explains the difference in the observed entropy for the Al(acetone) + system and those of other simple association reactions. Finally, direct clustering results from a newly constructed pulsed laser ionisation high pressure mass spectrometer are in excellent agreement with the Fourier transform mass spectrometry and ab initio findings.