W0328

The Role of the Aryl C-Br···X^- Synthon in the Crystal Structures of Copper(II) Halide Salts. Firas F. Awwadi, Roger D. Willett, Salim F. Haddad, and Brendan Twamley, Dept. of Chemistry, Washington State Univ., Pullman, WA 99164.

Recently, the halogen-halogen contacts have received much interest, due to their importance in crystal engineering as non-covalent interactions that link the structural units inside the crystal. Our interest has been in role that aryl C-Br···X^- (X=Cl^-, Br^-) interactions play in the determination of the crystal structures of copper(II) halide salts. In this context, many series of model structures have been determined. In the first one, we have investigated the crystal structures of tetrahalocuprates(II) with monobromopyridinium counterions (n-BrpyH)₂CuX₄, (X = Cl^- or Br, n = 2, 3, and 4). In all cases, low dimensional supramolecular networks are developed based on C-Br···X^- and N-H···X^- synthons. The C-Br···X^- synthon is invariably characterized by essentially linear C-Br···X angles with Br···X^- contacts 0.3-0.4 Å less than the sum of the van der Waals radii. The figure below shows these interactions and hydrogen bonds in (4-BrpyH)₂CuBr₄. In the second series, two types of dibromopyridinium cation have been used as counterions, [(2,5-dBrPyH)₂CuX₄] and [(3,5-dBrpyH)₂CuX₄]. The halogen-halogen contacts show an important role in the arrangement of the structural units inside the crystal. In another novel structure, these interactions led to the formation of the longest known planar bibridged oligomer, Cu₁₀X₂₂². To further investigate the relative roles of steric effects versus the Cu-Br···X^- synthon, we are studying the crystal structures of the analogous methyl substituted pyridine compounds