1-(4-TOLYSULFONYL)-1,4,8,11-TETRAAZACYCLOTETRADECANE (TSCYCLAM) - A VERSATILE LIGAND FOR NICKEL(II) AND NICKEL(III) CATIONS

1-(4-Tolylsulfonyl)-1,4,8,11-tetraazacyclotetradecane (Tscyclam, 3) forms complexes with Ni11 of stoichiometry: Ni(Tscyclam)X2-2H2O (X = Cl, ClO4). The crystal structure has been determined for the chloride complex salt, which indicates that the complex is better described by the formula [Ni(Tscyclam)(H2O)2]Cl2. The salt crystallizes in the monoclinic space group P21/n, with a = 13.030 (5) Å, b = 7.859 (3) Å, c = 22.640 (9) Å, β = 93.17 (3)°, V= 2315 (2) Å3, and Z = 4. The structure was solved by using 3062 unique reflections with I0 > 3σ(I0). Anisotropic least squares refinement gave R = 0.11. The tetraaza macrocycle is folded and the two water molecules occupy two cis positions of a distorted octahedron. Average distance for the Ni11(high spin)–N(amine) bonds is 2.08 (2) Å, whereas the Ni11(high sρin)–N(amide) distance is 2.36 (1) Å. The [Ni(Tscyclam)(H2O)2]2+ chromophore keeps intact its stereochemical arrangement on dissolution both in water and in noncoordinating solvents (e.g. CH2Cl2). Tscyclam has been used as a carrier for the transport of Ni11 across a bulk liquid membrane, displaying a much greater efficiency than the lipophilic version of cyclam (N-cetylcyclam, 2). The aqueous [NiII(Tscyclam)(H2O)2]2+ complex, in the presence of Cl− ions, is oxidized by persulfate to give the species [NiIII(Tscyclam)Cl2]+, in which two equivalent chloride ions lie on the z axis and the tetraaza macrocycle is coplanarly chelated, as shown by the ESR of the frozen solution. Coplanar coordination of Tscyclam is now allowed due to the smaller dimensions of the NiIII metal center compared to high-spin NiII. The NiIII/NiIII redox change could not be characterized through voltammetric investigations at the platinum electrode, but it was possible, through chemical evidence, to locate the potential for the [NiII(Tscyclam)Cl2]+/[NiII(Tscyclam)(H2O)2]2+ couple at an especially low value (<0.42 V vs NHE), much lower than that determined for the [NiIII(cyclam)Cl2]+/[NiII(cyclam)]2+ redox couple. © 1990, American Chemical Society. All rights reserved.