Understanding Cation–Anion Ionic Bonding in Tetramethylammonium Salts: Insights from Density Functional Theory and X-ray Crystallography

In describing the charge on tetraalkylammonium ions, a charge of +1 is usually assigned. This is both the actual charge as well as the "formal charge" which is usually written on the nitrogen atom to indicate the electron deficiency experienced by the nitrogen atom relative to the valence electrons. Nitrogen is the most electronegative atom in the ion. The results in this study show that despite the convention of writing the positive charge on nitrogen, the ion is polarized through the σ bond framework to present four tetrahedral faces, each having close to a full charge of +1 to any anionic species which approach the cation.