A comparative study of the DFT and MP2 methods on molecular structure of diphosphadithiatetrazocine

The B3LYP method based on the density functional theory (DFT) is shown to b e much better than the ab initio MP2 method for structural determination of diphosphadithiatetrazocine systems having transannular S---S bonding. The presence of bonding between the two sulfur atoms across the cyclic ring is theoretically confirmed in the case of the neutral diphosphadithiatetrazoci ne. The S---S bonding disappears in the ionized species. The planarity of t he dicationic heterocyclic ring system turns out to be closely associated w ith the pi-electron delocalization over the entire ring as well as the N-S- N bonds, which become stiffened upon ionization. In the case of dianionic s pecies, the chair-boat and chair conformers are nearly degenerate and far m ore stable than the crown conformer.