Defective Dicubane-like Tetranuclear Nickel(II) Cyanate and Azide Nanoscale Magnets

Four tetrameric nickel(II) pseudohalide complexes have been synthesized and structurally, spectroscopically, and magnetically characterized. Compounds 1-3 are isostructural and exhibit the general formula [Ni-2(dpk center dot OH)(dpk center dot CH3O)(L)(H2O)](2)A(2)center dot 2H(2)O, where dpk = di-2-pyridylketone; L = N-3(-), and A = ClO4- for 1, L = NCO- and A = ClO4- for 2, and L = NCO- and A = NO3- for 3. The formula for 4 is [Ni-4(dpk center dot OH)(3) (dpk center dot CH3O)(2)(NCO)](BF4)(2)center dot 3H(2)O. The ligands dpk center dot OH- and dpk center dot CH3O- result from solvolysis and ulterior deprotonation of dpk in water and methanol, respectively. The four tetramers exhibit a dicubane-like core with two missing vertexes where the Ni-II ions are connected through end-on pseudohalide and oxo bridges. Magnetic measurements showed that compounds 1-4 are ferromagnetic. The values of the exchange constants were determined by means of a theoretical model based on three different types of coupling. Thus, the calculated J values (J(1) = J(2), J(3), and D) were 5.6, 11.8, and 5.6 cm(-1) for 1, 5.5, 12.0, and 5.6 cm(-1) for 2, 6.3, 4.9, and 6.2 cm(-1) for 3, and (J(1), J(2), J(3), and D) 6.9, 7.0, 15.2, and 4.8 cm(-1) for 4.