Pyrazine-2-amidoxime Ni(II) complexes: from ferromagnetic cluster to antiferromagnetic layer.

Tetranuclear [Ni(4)(Hpzaox)(2)(pzaox)(2)(py)(4)](ClO(4))(2)·2py (1), [Ni(4)(Hpzaox)(2)(pzaox)(2)(py)(4)](NO(3))(2)·4py (2), and two-dimensional (2D) [Ni(4)(Hpzaox)(2)(pzaox)(2)(H(2)O)(2)](NO(3))(2)·2H(2)O (3) are prepared via the reaction of NiX(2)·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.

Ferromagnetic coupling in oximato-bridged multi-decker Ni(II) clusters.

Single-, double- and triple-decker oximato-bridged Ni(ii) clusters based on pyridine-2-amidoxime (H(2)pyaox) have been synthesized and characterized. The decks have the same tetranuclear cationic units [Ni(4)(Hpyaox)(2)(pyaox)(2)](2+) that are stably present in the reaction solution. Magnetic studies show that uncommon ferromagnetic exchange between the adjacent Ni(ii) ions through the oxime bridges is operative in the compounds with the magnetic coupling constant (J) in the range 0.