The complete halide series of Ni-II complexes containing the tetradentate macrocyclic ligand 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17), 13,15-triene (L), was fully characterized by X-ray diffraction. The fluoro, chloro, and bromo complexes are dinuclear species with formula [{Ni(L)}(2)(mu-X)(2)](2+) (X = halide), whereas only mononuclear species with formula [Ni(Y)(solv)(L)](n+) (Y = halide or solvent molecule), were obtained with I. To date, the fluoro derivative is the first nonorganometallic coordination compound containing the Ni(mu-F)(2)Ni core. The magnetic properties of these halo complexes have been studied. Intramolecular interactions were observed in the three dinuclear complexes, being antiferromagnetic in the fluoro derivative and ferromagnetic in both the chloro and bromo ones. The two iodo derivatives are paramagnetic species, as would be expected for mononuclear octahedral Ni-II complexes. Density functional theory calculations led us to relate the magnetic behaviors of these compounds to the values of the corresponding Ni-X-Ni-i angle. The analysis of the singly occupied molecular orbitals gave a clear comprehension of the different magnetic exchange interactions found in these Ni-II complexes.