121288-63-9Relevant academic research and scientific papers
Magnetic coupling in zero- and one-dimensional magnetic systems formed by nickel(II) and nitronyl nitroxides. Magnetic phase transition of a ferrimagnetic chain
Caneschi, Andrea,Gatteschi, Dante,Renard, Jean Pierre,Rey, Paul,Sessoli, Roberta
, p. 2940 - 2944 (2008/10/08)
Two novel compounds formed by nickel(II) hexafluoroacetylacetonate and nitronyl nitroxide radicals NITR = 2-R-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide, with R = methyl, Me, and phenyl, Ph, were synthesized. The compound Ni(hfac)2(NITPh)2 crystallizes in the monoclinic system, space group P21/c, with a = 12.243 (4) ?, b = 15.237 (4) ?, c = 22.310 (8) ?, β = 100.68 (2)°, and Z = 4. The nickel ions are octahedrally coordinated to two hfac molecules and to the oxygen atoms of two different radicals. The magnetic properties indicate the presence of a strong antiferromagnetic coupling between the nickel and the radicals, which has been roughly estimated to be on the order of 400 cm-1. Even if the structure of Ni(hfac)2NITMe is not available, we suggest an infinite chain structure, with each radical bridging two Ni(hfac)2 units, on the basis of analogies with other M(hfac)2NITR compounds. In agreement with the proposed structure, the magnetic susceptibility shows a divergence in the χT product at low temperature. A numerical fit, with a model previously used for Mn(hfac)2NITR ferrimagnetic chains, yields an antiferromagnetic coupling of 424 cm-1. The fast divergence of the susceptibility at very low temperature indicates the presence of a phase transition to three-dimensional order. Low-field (0-1 Oe) magnetic measurements show that the system undergoes a phase transition at ca. 5.3 K. The nature of the transition is presumably ferromagnetic and is driven by the dipolar interaction between chains, as in the analogous manganese-radical systems.
