Structures and N→Si Bond Characters of 1-Fluorosilatrane and the Silatranyl Cation

Abstract

The structures of 1-fluorosilatrane and the silatranyl cation were calculated by Hartree-Fock (HF), Mofller-Plesset second order (MP2), and various density functional theory (DFT) methods using many different basis sets, demonstrating that the Si-N bonds in two species are quite different. The N<TEX>${\rightarrow}$</TEX>Si bond distance of 1-fluorosilatrane from the hybrid DFT calculations <TEX>$({\sim}2.32{\AA})$</TEX> using the Perdew-Wang correlation functional agrees with the gas phase experimental value <TEX>$(2.324{\AA})$</TEX>, while other functionals yield larger distances. The MP2 bond distance (2.287<TEX>${\AA}$</TEX> with 6-311<TEX>$G^{\ast}$</TEX>) is shorter, and the HF one (2.544 <TEX>${\AA}$</TEX> with 6-311<TEX>$G^{\ast}$</TEX>) larger than those of DFT calculations. The MP2 bond distance is in good agreement with experiment indicating that the electron correlations are crucial for the correct description of the N<TEX>${\rightarrow}$</TEX>Si interaction. The silatranyl cation is a stable local minimum on the potential energy surface in all methods employed suggesting that the cation could be a reaction intermediate. The Si-N bond length for the cation is about 1.87 <TEX>${\AA}$</TEX> for all calculations tested implying that the Si-N bond is mainly conventional. Bonding characteristics of the Si-N bond in two species derived from the natural bond orbital analysis support the above argument based on calculated bond lengths.