The reactivity of the phosphomacrocycle 6-phenyl-15-aza-6-phospha-3,9-dithiabicyclo[9,3,1]pentadeca-1(15), 11,13-triene (L) toward different Ni(II) salts has been studied. The reaction of L with 1 molar equiv of Ni(II) perchlorate in acetonitrile solution gives the complex [Ni(L)(CH3CN)(2)](ClO4)(2) (1), which crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 12.704(2) Angstrom, b = 13.538(2) Angstrom, c = 17.377(2) Angstrom, beta = 107.554(8)degrees, and Z = 4. The Ni(II) atom in 1 shows an octahedral environment defined by the four donor atoms of L and two acetonitrile molecules in a cis disposition. The reaction of L with Ni(II) perchlorate in 2:1 molar ratio yields the green complex [Ni(Lox)(2)](ClO4)(2) (2) in which the phosphine groups of the ligand L are in their phosphine-oxide form (Lox). The same complex is also obtained by adding more ligand L to an acetonitrile solution of 1. Complex 2 crystallizes in the triclinic space group P (1) over bar (No. 2) with a = 10.564(1) Angstrom, b = 11.975(2) Angstrom, c = 9.124(2) Angstrom, alpha = 109.79(1)degrees, beta = 95.67(2)degrees, gamma = 109.19(1)degrees and Z = 1. The octahedral coordinated Ni(II) atom in 2 lies on a crystallographic center of symmetry, and it Is surrounded by two pyridine nitrogen atoms, two thioether sulfur atoms, and two phosphine-oxide oxygen atoms provided by two facially coordinated Lox ligands. The reaction of L with NI(II! chloride and Ni(II) thiocyanate yields the complexes [NiCl2(L)] (3) and [Ni(NCS)(2)(L)] (4), respectively, which are also obtained by adding Me4NCl or KSCN to an acetonitrile solution of 1. Complex 4 crystallizes in the monoclinic space group P2(1)/n (No. 14), with a = 11.139(2) Angstrom, b = 13.270(2) Angstrom, c = 14.885(1) Angstrom, beta = 92.34(1)degrees, and Z = 4, and its structure is similar to that of complex 1, simply replacing the two acetonitrile molecules by two SCN- anions. The reactions of the complex 1 with different chelating ten, bipy, o-phen) and nonchelating (py) N-donor ligands have also been carried out. In all cases the two acetonitrile molecules of 1 are easly replaced by the N-donor ligands, but the macrocycle L molecule remains coordinated to the Ni(II) atom. The crystal structure of the complex [Ni(L)(py)(2)](ClO4)(2) (5) is also elucidated. Crystal data : monoclinic space group P2(1)/c (No. 14) a = 13.063(2) Angstrom, b = 16.615(3) Angstrom, c = 14.973(3) Angstrom, beta = 91.76(2)degrees, Z = 4.