Two new cobalt(II) complexes of formula [Co(hfac)2(NITphtrz) 1 and Co(hfac)2(IMphtrz) 2] have been prepared and characterized structurally [where NITphtrz = 4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazoline-1-oxyl-3-oxide and IMphtrz = 4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazoline-1-oxyl]. All of the complexes crystallize in an isomorphous triclinic space group with the Co(II) ion octahedrally coordinated via the bidentate chelating mode. The magnetic measurements show that two complexes exhibit antiferromagnetic interactions between the metal ions and the nitroxide radicals. 1. Introduction Metal-radical complexes have been well investigated toward molecule-based magnets, where a radical center is directly bonded to the metal ion and affording appreciable magnetic exchange coupling [1]. The predominant magnetic features of metal-nitroxide complexes are determined by the donor properties of the nitronyl group and the coordination geometry of the resulting complex. In the past decades, growing interest has been paid to metal complexes with nitronyl nitroxide (NITR: 4,4,5,5-tetramethyl-2-R-imidazolin-1-oxyl-3-oxide) and imino nitroxide (IMR: 4,4,5,5-tetramethyl-2-R-imidazolin-1-oxyl) radicals [2–5]. The feature of R-group linked to the nitronyl nitroxide not only influences the intermolecular spin-spin interactions but also affects the coordination mode of the nitronyl nitroxides with metal ions [6, 7]. Because the auxiliary heteroaromatic N-donor forces the nitroxide O-atom to bind to a poor electrophilic metal center by the chelating effect, the complexes of nitronyl or imino nitroxides substituted by N-heteroaromatic groups have drawn great interests. Cobalt(II) complexes have been rarely investigated due to large spin-orbital coupling, although cobalt(II) is a very effective spin carrier. In order to extend our knowledge of the extremely rich chemistry of such systems, it was thus of interest to further explore the reactions between Co(hfac)2 and nitroxide radicals. In this paper, we will report two new nitroxide ligands L1 and L2 (Scheme 1). Due to the presence of the N-triazole moieties, L1 and L2 can coordinate to metal ions as chelate ligands. Reactions of L1 and L2 with Co(hfac)2 (hfac = hexafluoroacetylacetonate) afforded two heterospin complexes. Crystal structures and magnetic properties of the related compounds (Co(hfac)2(NITphtrz) 1 and Co(hfac)2(IMphtrz) 2) will be described and discussed. Scheme 1 2. Experimental 2.1. Materials and Equipment 2-phenyl-1,2,3-triazole-4-carboxaldehyde was prepared according to
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