The novel pyridine-containing 14-membered macrocycle 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,-15-triene (L), which contains an N2S2 donor set, was synthesized, and its protonation behavior was studied by absorption titration with CH3SO3H. The reaction of L with Pd(II) was studied spectroscopically, and the square-planar complex [Pd(L)](BF4) was isolated and characterized. The reactions between L and NiX(2)center dot 6H(2)O (X = BF4,ClO4) in ethanol or acetonitrile afforded the octahedral complexes [Ni(CH3CN)(H2O)(L)](X)(2) and [Ni(H2O)(2)(L)](X)(2), respectively. The square-planar complexes [Ni(L)](X)2 were obtained by heating these octahedral complexes. Spectrophotometric titrations of [Ni(L)](BF4)(2) were performed with neutral and negatively charged ligands. The color of nitromethane solutions of this square-planar complex turns from red to cyan, purple, blue, yellow-green, and pink following addition of halides, acetonitrile, water, pyridine, and 2,2'-bipyridine, respectively. X-ray structural analyses were carried out on the {[Ni(ClO4)(H2O)(L)][Ni(H2O)(2)(L)]}(ClO4)(3), [Ni(CH3CN)(H2O)(L)](ClO4)(2), [{Ni(L)}(2-)(mu-Cl)(2)](ClO4)(2), and [{Ni(L)}(2)(mu-Br)(2)]Br(2)center dot(2)CH(3)NO(2) complexes.