Theoretical studies on ion pairs. An ab-initio investigation of the lithium–formaldehyde ion pair

Abstract

The lithium–formaldehyde ion pair has been investigated by an ab-initio MO–SCF–UHF treatment. The computations have been carried out at two different levels of sophistication. A detailed search of the energy surface of this system has been made at the STO-3G level, by optimizing the Li–O bond lengths at various directions of cationic attack. At this computational level two minima were found; we then reinvestigated the two minima with an STO-6G basis set. In the more stable species (A) the Li⁺ is 1·46 Å from the oxygen atom on the C–O bond axis, while in the other stable species (B) Li⁺ is 1·61 Å above the oxygen atom. In species (A) the bond between the cation and the anion has a dominant π character, while in species (B) the bond has mainly σ character.