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-propan ediol di-p-tosylate with dioxocyclam. The corresponding Ni(II) complex, Ni( dc3), has been prepared and structurally characterized by X-ray crystallogr aphy. In addition, the structure of the dioxocyclam complex of Ni(II), Ni(d c), 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 constrain t 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) t han in Ni(dc) (0.039(1) Angstrom), resulting in a lower than expected ligan d field strength for Ni(dc3). The arrangement of the three carbon straps an d their potential to interact with the metal center are also discussed. (C) 1999 Elsevier Science S.A. All rights reserved.