The N,N,N-trimethylammonium moiety as tetrel bond donor site: crystallographic and computational studies

Five structures bearing the N,N,N-trimethylammonium unit have been investigated to address the ability of the N⁺-CH₃ unit to function as a tetrel bond donor site. Charged and neutral electron density donors display close contacts with different carbon atoms of methyl groups on the ammonium moiety. The Hirshfeld atom refinement (HAR) technique was used on selected structures to accurately and precisely determine the hydrogen atom positions and, consequently, to get better insights into the N⁺-C⋯Nu (Nu = nucleophile) interactions occurring in the crystals. In particular, the performed analyses highlighted specific geometrical features of the moieties involved in the interactions and allowed distinguishing between tetrel and hydrogen bonds.