Revision of the Crystal Structure of the Orthorhombic Polymorph of Oxyma: On the Importance of pi-Hole Interactions and Their Interplay with H-Bonds

In this work the crystal structure of the previously described orthorhombic polymorph of the coupling reagent Oxyma has been revised, corrected now as centrosymmetric and analyzed by means of DFT calculations. In the solid state the structure forms a network of H-bonds and self-assembled dimers that are held together by the formation of N center dot center dot center dot C pi-hole interactions involving the C-atom of the imino group. The H-bonding and pi-hole interactions observed in the solid state were rationalized using molecular electrostatic potential (MEP) surfaces, focusing on the H-bond donor-acceptor groups and the pi-hole observed above and below the molecular plane. The interactions and their interplay have been characterized by using two methodologies based on the topology of the electron density, which are the quantum theory of "atom-in-molecules" (QTAIM) and the noncovalent interaction plot (NCIplot).