The deprotonated form of the pyrazine-2,3-diselenol (pds) ligand, pds(2-), reacts with Ni-II inorganic salts to form the nickel compounds [Ni-II(pds)(2)](nBu(4)N)(2) (1), [Ni-II(pds)(2)]Na-2.2H(2)O (2), and [Ni-III(pds)(2)](2)Na-2.4H(2)O (3), depending on the reaction conditions. They are characterized by NMR, EPR, UV-vis, and IR spectroscopies, elemental analysis, cyclic voltammetry, and X-ray crystallography. The crystal structure of compound 3 shows the formation of segregated stacks of Ni(pds)(2)(-) units, with a strong dimerization along the stacks. The stacked fashion of the crystal packing was expected since the supramolecular forces of the alkaline side coordination to the pyrazine moieties dominate, as happens in the recently reported analogous copper system [Cu-III(pds)(2)]Na.2H(2)O. The structure of 2 further emphasizes the alkaline coordination as the dominating supramolecular event, and an orthogonal array of 2D layers is observed. The absence of alkaline cations in complex 1 is reflected in a crystal packing with isolated complex Ni(pds)(2)(2-) units. The dimerization found in the paramagnetic Ni-III complex 3 promotes a very strong antiferromagnetic interaction, leading to a singlet ground state.