Exploring {2}-metallacryptands and {2}-metallacryptates with quantum chemical methods - When (not only) computer chemists' dreams come true

Semiempirical PM3 computations are reported for the {2}-gallium cryptand an d {2}-gallium cryptates with three 2,6-bis(acetylaceto)pyridine ligands. Op timized "sparkles" are employed for the description of metal ion guests for which no PM3 parameters are available. Calculated structures agree well wi th available X-ray structures of the corresponding {2}-iron cryptates. The trend in the computed complexation energies of the guest metal ions, compar ed to solvent complexes, agrees with experimental findings: for experimenta lly known complexes, exothermic exchange is computed, while endothermic exc hange is calculated for cryptates that could not be synthesized. In the cas e of lead, the predicted favorable cryptate formation subsequently was veri fied experimentally.