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 0.6-6.3 cm(-1) (H = -2JS(Ni1)S(Ni2)). Density function theoretical (DFT) calculations and the experimental data confirm that the N-O bond distances of the bridging oxime group have a decisive effect in magnetic coupling. For the present Ni(ii) species, the elongation of N-O bond distances are responsible for the switching from antiferromagnetic to ferromagnetic exchange with the critical bond distance of 1.394 Å.