文摘
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 [Ni2(dpk·OH)(dpk·CH3O)(L)(H2O)]2A2·2H2O, where dpk = di-2-pyridylketone; L = N3−, 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 [Ni4(dpk·OH)3 (dpk·CH3O)2(NCO)](BF4)2·3H2O. The ligands dpk·OH− and dpk·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 NiII 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 (J1 = J2, J3, 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 (J1, J2, J3, and D) 6.9, 7.0, 15.2, and 4.8 cm−1 for 4.