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The synthesis and magnetism of nitroxide radicals and their metal complexes
This work has involved the synthesis, crystallographic and magnetic study of several stable t-butyl nitroxide radicals and their coordination complexes. They formed various stable coordination complexes with transition metal hexafluoroacetylacetonates. The crystal structure of each magnetically studied radical and complex was examined in detail for magnetic exchange pathways. The radicals themselves showed through-space magnetic exchange interactions that resulted in weak low temperature exchange. The complexes had strong room temperature magnetic exchange between the coordinated nitroxide radical and the paramagnetic metal, with relatively weak exchange between these spins units which was explain by orbital interactions and spin polarization, respectively. The molecules that were studied included, 5-(4-[N-tert-butyl- N-aminoxyl]phenyl)pyrimidine which was isolated as a stable crystalline solid that formed hydrogen bonded anti-parallel chains. The magnetic susceptibility data above 10 K was fit to an alternating Heisenberg AFM chain. This nitroxide radical formed various stable coordination complexes with transition metal hexafluoroacetylacetonates (hfac), namely 1:1 cyclic dimers, 2:1 dimers and a 2:3 coordination polymer. The Mn(II) and Cu(II) 1:1 cyclic dimers showed strong AFM and FM exchange coupling (respectively) between the coordinated paramagnetic ion and the nitroxide unit. The magnetic susceptibility data for the Mn(II) and Cu(II) 1:1 cyclic dimers were fit to a dimer model. The 2:1 dimer complexes were composed of two 5-(4-[N-tert-butyl- N-aminoxyl]phenyl)pyrimidine molecules coordinated at the pyrimidine nitrogen to a metal hfac cation [Mn(II), Ni(II), Cu(II) and Co(II)]. The complexes studied show paramagnetic behavior at room temperature of three spins. The magnetic susceptibility data for the Ni(II) and Cu(II) complexes were fit to a dimer model. A crystal lographically similar Zn(II) complex was fit to a 2-D dimer model. The Co(II) 2:3 coordination polymer showed room temperature AFM exchange between the nitroxide and Co(II) ions. N-Tert-butyl-N-(4-[1,2,4]triazol-1-yl-phenyl)-aminoxyl was also a stable radical that formed Mn(II), Ni(II), Co(II) and Cu(II) 1:1 cyclic dimer complexes. The Mn(II), Ni(II) and Co(II) complexes showed room temperature AFM interactions between the metal ion and the nitroxide unit and were fit to a dimer model. 4-(N-Tert-butyl-N-aminoxyl)-1,1-biphenyl-3 ′,5′-dicarboxylic acid was isolated as a stable crystalline solid that formed hydrogen bonded chains. The magnetic susceptibility was fit to a Bonner-Fischer chain model.
Field, Lora Marie, "The synthesis and magnetism of nitroxide radicals and their metal complexes" (2003). Doctoral Dissertations Available from Proquest. AAI3096275.