POLYMERIC 1,7-DITHENYLIDENE-1,4,7-TRIAZAHEPTANE COPPER(II) CHLORIDE WITH EXTENDED LINEAR STRUCTURE

The crystal and molecular structures of [Cu-3(dienSS)(2)Cl-6] where dienSS is a Schiff base 1,7-dithenylidene-1,4,7-triazaheptane are reported. The compound is polymeric with extended linear structure; it has a trimeric repeating unit in which two edge-sharing pseudooctahedral groups [Cu(dienSS)Cl-3](-) are linked by single Cl bridges to a highly distorted tetrahedral [CuCl4](2-) group. The space group is Pbcn, Z = 4 with a = 13.979(2), b = 20.567(2), c = 12.9481(9) Angstrom , DienSS, a potentially pentadentate ligand coordinates to Cu-II as tridentate with dangling thiophene residues; it is located normal to the Cu-Cu axis with CuN = 2.026(7), 2.021 (7) and 2.024(7) A. The three CuCl bonds completing Cu(dienSS) to a pseudooctahedron differ in length and position: CuCl = 2.253(2) Angstrom is in the same plane as the three CuN; CuCl = 3.029(2) Angstrom is perpendicular to that plane and takes part in the double bridge Cu(Cl)(2)CU; CuCl = 3.133 Angstrom takes part in a single bridge with the [CuCl4](2-) group. The [CuCl4](2-) group is closer to a planar structure than to a tetrahedron: trans-ClCuCl angles are 154.0(2) and 157.2(2)degrees. The CuCl bonds are 2.286(2) Angstrom (bridging to two different six-coordinate Cu units) and 2.226(3) Angstrom (free). Both the elongated pseudooctahedra and the planar structure are due to vibronic coupling. Molecular mechanics (MM), Austin Model 1 (AM1) and extended Huckel (EH) calculations suggest that electron delocalization to the thiophene groups occurs upon coordination.