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

<i>N</i>,<i>N</i>-Dipyridilaminoxyl, <b>NOpy</b>_<b>2</b>, having a stable aminoxyl, was prepared as a new magnetic coupler for heterospin systems. Solutions of <b>NOpy</b>_<b>2</b> 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(<b>NOpy</b>_<b>2</b>)]_<i>n</i>; X = H (<b>1</b>), F (<b>2</b>), F₃ (<b>3</b>), F₅ (<b>4</b>), Cl (<b>5</b>), Cl₃ (<b>6</b>), Br (<b>7</b>), and I (<b>8</b>) as single crystals. In all complexes, the local structures of the cobalt-complex units were compressed octahedra and the pyridine ligands in <b>NOpy</b>_<b>2</b> units coordinated to the cobalt ions in trans configuration to form linear chains for <b>1</b>–<b>4</b> and in cis configuration to form helical chains for <b>5</b>–<b>8</b>. In the chains, the aminoxyl in <b>NOpy</b>_<b>2</b> ferromagnetically interacted with the cobalt ions to produce the ferromagnetic chains with <i>J</i>_intra/<i>k</i>_B = 9–14 K. In the magnetic susceptibility experiments of aligned sample of <b>6</b>, the magnetic easy axis was determined to be the <i>a</i>* axis, which was the direction perpendicular to the <i>b</i> axis of the chain axis. The resulting chains, all except <b>4</b>, interacted antiferromagnetically among each other, and especially in <b>1</b>, <b>5</b>, <b>7</b>, and <b>8</b>, the magnetic behaviors characteristic to canted two-dimensional (2D) antiferromagnets with <i>T</i>_c = 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, Δ_eff/<i>k</i>_B, for the reorientation of the magnetism for all complexes except <b>4</b> were estimated to be 25–39 K in the presence of a direct current (dc) field