Chelate effect: The importance of reorganization energy

The chelate effect has been theoretically studied at the Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Paar/double-ζ polarization level of theory. The influence of ligand, metal, and halogen nature on the chelate effect was analyzed for complexes of group 14 element tetrahalides with monodentate and bidentate nitrogen-containing donors. It is shown that the large reorganization energy of the 2,2′-bipyridine ligand (≈32 kJ mol^-1) shadows the chelate effect. The same conclusion holds for other ligands, which undergo significant reorganization upon complex formation. 1,10-Phenanthroline does not have such a large reorganization energy, and its complexes are therefore more stable in the gas phase than are complexes with bipyridine.