A new structurally constrained dioxocyclam ligand: synthesis, characterization and molecular structure comparison of its nickel(II) complex with the nickel(II) complex of dioxocyclam

The structurally constrained dioxocyclam ligand, 1,4,8,11-tetraazabicyclo[9.3.3]heptadecacane-5,7-dione, H(2)dc3, was prepared by refluxing 1,3-propanediol di-p-tosylate with dioxocyclam. The corresponding Ni(II) complex, Ni(dc3), has been prepared and structurally characterized by X-ray crystallography. In addition, the structure of the dioxocyclam complex of Ni(II), Ni(dc), has been determined for comparison with Ni(dc3). In both cases, the Ni(II) sits in a square planar array of four nitrogens. However, the constraint imposed by the additional trimethylene strap in Ni(dc3) causes the Ni(II) to be farther out of the plane of the four nitrogens (0.089(1) Angstrom) than in Ni(dc) (0.039(1) Angstrom), resulting in a lower than expected ligand field strength for Ni(dc3). The arrangement of the three carbon straps and their potential to interact with the metal center are also discussed. (C) 1999 Elsevier Science S.A. All rights reserved.