Multiple Noncovalent Bonding in Halogen Complexes with Oxygen Organics. I. Tertiary Amides

The present work describes the structure and binding of adducts of N,N′-diacetylpiperazine with halogens and interhalogens based on combination of different experimental methods and quantum chemical calculations. On the basis of conductometric and spectro-photometric experimental results, behavior of complexes in the acetonitrile solution was described. The iodine adduct with N,N′-diacetylpiperazine fully degrades into components. Adducts of interhalogens I–X (X = Cl or Br) with N,N′-diacetylpiperazine in acetonitrile partially dissociate to anionic [X–I–X]− and cationic species. In the solid state, molecules are connected via CO···I, C–H···I, and Cl···Cl attractive interactions. N,N′-diacetylpiperazine···dihalogen complex is stabilized by simultaneous CO···I and C–H···I interactions. Such binding mode allows to explain the problems of the direct halogenation of acetyl-containing compounds with molecular halogens as reagents. We believe that the observed binding pattern can be used as prototypical for future design of halogeno complexes.