The nickel() complex of the naphthalene-containing macrocyclic ligand 4 has been synthesized by a template reaction and structurally characterized. [Ni(4)] 2+ , which in solution displays an emission spectrum typical of naphthalene derivatives, undergoes a reversible one-electron reduction process at a moderately negative potential value to give a formal nickel() species. The reduction process induces a distinct decrease of the emission intensity, but fluorescence is recovered after reoxidation to the original nickel() species. Thus, fluorescence can be switched OFF and ON through the redox reaction involving the formal Ni II /Ni I couple, which can be carried out both chemically (in MeCN : water) and electrochemically (in MeCN).

1 -(4-Tolylsulfonyl)-1,4,8,11 -tetraazacyclotetradecane (Tscyclam, 3) forms complexes with Ni" of stoichiometry: Ni(Tscyclam)X2.2H20 (X = CI, C104). The crystal structure has been determined for the chloride complex salt, which indicates that the complex is better described by the formula [Ni(Tscy~lam)(H~O)~]CI~. The salt crystallizes in the monoclinic space group P2,/n, with a = 13.030 ( 5 ) A, b = 7.859 (3) A, c = 22.640 (9) A, 0 = 93.17 (3)O, V = 2315 (2) A', and Z = 4. The structure was solved by using 3062 unique reflections with Io > 30(10). Anisotropic least squares refinement gave R = 0.1 I. The tetraaza macrocycle is folded and the two water molecules occupy two cis positions of a distorted octahedron. Average distance for the Ni"(high spin)-N(amine) bonds is 2.08 (2) A, whereas the Ni"(high spin)-N(amide) distance is 2.36 ( I ) A. The [Ni(Tsc y~l a m ) ( H~O )~]~+ chromophore keeps intact its stereochemical arrangement on dissolution both in water and in noncoordinating solvents (e.g. CHzC12). Tscyclam has been used as a carrier for the transport of Ni" across a bulk liquid membrane, displaying a much greater efficiency than the lipophilic version of cyclam (N-cetylcyclam, 2). The aqueous [Ni11(Tscyclam)(H20)2Jz+ complex, in the presence of CI-ions, is oxidized by persulfate to give the species [Ni"1(Tscyclam)C12]+, 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 Nil1' metal center compared to high-spin Nil1. The Ni"'/Ni" 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 [Ni~~1(Tscyclam)CIz]~/[Ni~~(Tscyclam)(H20)z]z~ couple at an especially low value (<0.42 V vs NHE), much lower than that determined for the [Ni"l(cyclam)C1z]+/[Nil~(cyclam)]z+ redox couple. (3) Fabbrizzi, L.; Forlini, F.; Perotti, A.; Seghi, B. Inorg. Chem. 1984, 23, 807. Buttafava, A.; Fabbriui, L.; Perotti, A.; Poggi, A,; Seghi, B. Inorg.

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