Calculation of stacking geometries by a modified MM2 method

The MM2 method has been modified using a three-center charge model aimed at determining stacking geometries. The stacking interactions for the benzene dimer; porphine dimer, and bis(4,5-diazafluoren-9-one thiosemicarbazonato) palladium(II) have been assessed with both the three-center charge model an d the conventional single-center charge model using the MM2 method. The mod ified MM2 method always gave better results than the conventional method, a nd the obtained structures by the former method are in good agreement with the proposed structures from those theoretical and experimental results. Th e possible advantages of using the three-center charge model for complex sy stems are also discussed. (C) 2001 John Wiley & Sons, Inc.