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Preparations, Crystal Structures, and Magnetic Properties of N,N-Dipyridylaminoxyl as a New Magnetic Coupler and Its One-Dimensional Cobalt(II) Chains

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posted on 07.05.2012, 00:00 by Kensuke Murashima, Takeaki Watanabe, Shinji Kanegawa, Daisuke Yoshihara, Yuji Inagaki, Satoru Karasawa, Noboru Koga
N,N-Dipyridilaminoxyl, NOpy2, having a stable aminoxyl, was prepared as a new magnetic coupler for heterospin systems. Solutions of NOpy2 were mixed with those of bis­{1,1,1,5,5,5, hexafluoro-4-(phenylimino)-2-pentanonate}­cobalt derivatives, Co­(hfpip-X)2, at a 1:1 ratio to afford the polymeric cobalt­(II) complexes, [Co­(hfpip-X)2(NOpy2)]n; X = H (1), F (2), F3 (3), F5 (4), Cl (5), Cl3 (6), Br (7), and I (8) as single crystals. In all complexes, the local structures of the cobalt-complex units were compressed octahedra and the pyridine ligands in NOpy2 units coordinated to the cobalt ions in trans configuration to form linear chains for 14 and in cis configuration to form helical chains for 58. In the chains, the aminoxyl in NOpy2 ferromagnetically interacted with the cobalt ions to produce the ferromagnetic chains with Jintra/kB = 9–14 K. In the magnetic susceptibility experiments of aligned sample of 6, the magnetic easy axis was determined to be the a* axis, which was the direction perpendicular to the b axis of the chain axis. The resulting chains, all except 4, interacted antiferromagnetically among each other, and especially in 1, 5, 7, and 8, the magnetic behaviors characteristic to canted two-dimensional (2D) antiferromagnets with Tc = 5.6, 4.0, 4.0, and 6.2 K, respectively, were observed. All complexes showed slow magnetic relaxations affected by the interchain antiferromagnetic interaction. The effective activation barriers, Δeff/kB, for the reorientation of the magnetism for all complexes except 4 were estimated to be 25–39 K in the presence of a direct current (dc) field.