Dichlorine-pyridine N-oxide halogen-bonded complexes

A new Cl-Cl···−O-N+ halogen-bonded paradigm has been demonstrated, using dichlorine as a halogen bond (XB) donor and N-oxide as an XB acceptor. Their crystalline complexes were formed during the warm-up process from −196 °C to −80 °C for X-ray diffraction analysis. They exhibit high instability in the crystalline state, even at these low temperatures, leading to rapid decomposition and the formation of Cl⋯H-O-N hydrogen-bonded complexes. The normalized XB interaction ratio (RXB) of Cl⋯O interactions in the solid-state demonstrates affinity comparable to traditional I⋯O interactions observed in I-I···−O-N+ halogen-bonded systems. The Cl-Cl⋯O XB angles vary from 172° to 177°, manifesting the structure-guiding influence of the electronegative chlorine atom's σ-hole on these XB interactions. © 2024 The Royal Society of Chemistry.