Competition between Hydrogen and Halogen Bonding Interactions: Theoretical and Crystallographic Studies

Abstract

Crystal structures of six iodopyridinium tetrahalocuprate(II) salts are reported, (nIP)2CuX4, where X = Cl or Br, nIP is the n-iodopyridinium cation, and n = 2, 3, or 4. The supramolecular structure of these salts is developed based on N–H···X hydrogen bonding and C–I···X halogen bonding interactions. Comparing these structures with the previously published structures of the general formulas (nCP)2CuX4 and (nBP)2CuX4, where nCP+ and nBP+ are the n-chloropyridinium and n-bromopyridinium cations, respectively, allows us to investigate the competition between the halogen and hydrogen bonding interactions. Henceforth, the general formula (nYP)2CuX4 will be used to represent the 18 structures where nYP+ is the n-halopyridinium cation. Isomorphism has been observed in these structures. Isomorphic structures are divided into four sets. Analysis of the isomorphic structures allows us to apply the separation of variables principle; upon comparison of isomorphic structures, complications arise from geometrical fact...