FERROMAGNETIC BEHAVIOR OF NICKEL(II)-IMINO NITROXIDE DERIVATIVES

Nickel(II) hexafluoroacetylacetonate derivatives of imino nitroxides have been synthesized and structurally characterized. In complex 1, diaquobis(2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl)bis)hexafluoroacetylacetonato)nickel(II), Ni(hfac)2(H2O)2(IMPh)2, the phenyl-substituted free radical is not coordinated to the metal but hydrogen bonded to the aquo metal fragment. On the other hand, in 2, (2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl)bis(hexafluoroacetylacetonato)nickel(II), Ni(hfac)2IM2-Py, and 3, bis(2,4,4,5,5-pentamethyl-4,5-dihydro-1H-imidazol-1-oxyl)bis(hexafluoroacetylacetonato)nickel(II), Ni(hfac)2-(IMMe)2, the 2-pyridyl and methyl-substituted ligands are bound to the Ni(II) ion through the imino nitrogen atom. Magnetic susceptibility measurements show that the metal-radical exchange interaction is ferromagnetic and fairly large (94 and 59 cm-1 for 2 and 3, respectively) in the N-bonded compounds, while the interaction mediated by the hydrogen bond in 1 is weakly antiferromagnetic. These results are rationalized in the frame of the natural magnetic orbital model. Relevant structural data are as follows: 1, space group P2(1)/n, a = 11.700 (3) angstrom, b = 17.928 (4) angstrom, c = 11.171 (3) angstrom, beta = 107.92 (2)-degrees, Z = 2; 2, space group P1BAR, a = 9.277 (3) angstrom, b = 12.984 (3) angstrom, c = 13.599 (3) angstrom, alpha = 95.03 (1)-degrees, beta = 109.17 (1)-degrees, gamma = 110.74 (1)-degrees, Z = 2; 3, space group P1BAR, a = 10.895 (3) angstrom, b = 10.934 (3) angstrom, c = 14.307 (3) angstrom, alpha = 82.77 (1)-degrees, beta = 84.33 (1)-degrees, gamma = 85.77 (1)-degrees, Z = 2.