1,4,7-Trithiacyclononane, a Novel Tridentate Thioether Ligand, and the Structures of Its Nickel(II), Cobalt(II), and Copper(II) Complexes

An improved method for preparing 1,4,7-trithiacyclononane (1,4,7-TTCN) is reported. The yields of certain medium-sized-ring dithioethers are also improved by this method. The bis(1,4,7-trithiacyclononane)nickel(II), -cobalt(II), and -copper(II) complexes have been prepared and their structures determined by X-ray crystallographic analyses. The [Ni(1,4,7-TTCN)₂](BF₄)₂ complex crystallizes in the monoclinic space group P2₁/c with a = 8.681 (2) Å, b = 11.685 (3) Å, c = 11.624 (3) Å, β = 106.57 (2)°, and Z ≈ 2. The [Co(l,4,7-TTCN)₂](BF₄)₂ complex crystallizes in the orthorhombic space group Pbca with a = 19.789 (40) Å, b = 15.235 (12) Å, c = 9.202 (3) Å, and Z = 4. The [Cu(l,4,7-TTCN)₂](BF₄)₂ complex crystallizes in the orthorhombic space group Pbca with a = 21.169 (3) Å, b = 15.193 (2) Å, c = 8.729 (2) Å, and Z = 4. Full-matrix least-squares refinement led to convergence with R = 0.030, 0.094, and 0.062, respectively, after several cycles of anisotropic refinement. In each complex the metal atom occupies a slightly distorted octahedral environment of sulfur atoms provided by two facially coordinating 1,4,7-TTCN ligands. The geometrical constraints of the ligand induce nearly regular octahedral coordination even with copper(II).