1. Half-Sandwich Structure of Cyclopentadienyl Dialuminum
Dong-Sheng Yang, Department of Chemistry, University of Kentucky
Four isomeric structures of Al2Cp, with two Al atoms residing on the same
or opposite sites of the Cp plane, are predicted by second-order Møller-
Plesset perturbation theory. A mixed-valent half-sandwich structure of
this complex (d, -Al2Cp) is identified by the experiment.
(a) Al-Cp-Al (b) h-Al2Cp
(c) t-Al2Cp (d) v-Al2Cp
In this structure, an Al atom is directly bound to the Cp ligand in a fivefold mode, whereas the other Al atom acts like a spectator. The ground electronic states of the neutral and ionized Al2Cp are 2A" in Cs symmetry and 1A1 in C5v symmetry, respectively. The metal-ligand bonding consists of orbital and electrostatic contributions. Ionization of the 2A" neutral state enhances the metal-ligand bonding, but weakens the metal-metal interaction.