Tetranuclear [Ni-4(Hpzaox)(2)(pzaox)(2)(py)(4)](ClO4)(2)center dot 2py (1), [Ni-4(Hpzaox)(2)(pzaox)(2)(py)(4)](NO3)(2)center dot 4py (2), and two-dimensional (2D) [Ni-4(Hpzaox)(2)(pzaox)(2)(H2O)(2)](NO3)(2)center dot 2H(2)O (3) are prepared via the reaction of NiX2 center dot 6H(2)O and pyrazine-2-amidoxime (H(2)pzaox). All compounds contain [Ni-4(Hpzaox)(2)(pzaox)(2)](2+) fragments, which assemble to form a tetranuclear or polymeric network. Magnetic studies show that the tetranuclear compounds display usual ferromagnetic coupling via the oxime N-O bridges, and the 2D compound displays unusual antiferromagnetic behavior.