Four-Center Six-Electron Interaction versus Lone Pair−Lone Pair Interaction between Selenium Atoms in Naphthalene Peri Positions

Abstract

The X-ray crystallographic analysis of bis[8-(phenylselanyl)naphthyl]-1,1‘-diselenide (1) and 1-(methylselanyl)-8-(phenylselanyl)naphthalene (2) showed that the four selenium atoms in 1 aligned linearly, while the Se−C(Me) and Se−C(Ph) bond in 2 declined by about 50° and 40° from the naphthyl plane, respectively. Ab initio molecular orbital calculations were performed on the models of 1 and 2, model a (HbHc2Se···Ha1Se3SeHa···4SeHbHc) and model b (HaHb1Se···2SeHa‘Hb‘), respectively, with the 6-311++G(3df,2pd) basis sets at the HF and MP2 levels, and the calculations reproduced well the observed structures and revealed the nature of the bonds constructed by the selenium atoms containing nonbonded interactions. The bond with four linearly aligned selenium atoms in model a can be analyzed with the 4c-6e model constructed with the nonbonded interaction between the two p-type lone pairs on the outside selenium atoms and the σ*(Se−Se) orbital of the inside Se−Se bond, which results in charge transfer from the outside Se atoms to the inside Se atoms. The nonbonded interaction between the two p-type lone pairs at the Se atoms in model b is analyzed as a π-type 2c-4e bond. The bent structure in Hb-1Se···2Se−Hb‘ was demonstrated to be the result of the requirement to avoid the severe exchange repulsion between the filled p-type lone pairs at the two selenium atoms. The calculations on the other models, PhSeH···HSeSeH···HSePh and PhSeH···HSeMe, with the 6-311+G(d,p) basis sets at the DFT (B3LYP) level showed that the π-orbitals of the phenyl groups of the former interacted effectively with the 4c-6e orbitals but the π-orbitals of the latter did little with the 2c-4e orbitals due to the orthogonality of the two systems.