Magnetic Properties of 1:4 Complexes of CoIIX2 (X = NCO−, NCS−, and Br−) with 4-(<i>N</i>-<i>tert</i>-Butylaminoxyl)pyridine. Antiferromagnets in Crystalline States and Single-Molecule Magnets in Frozen Solutions

DOI PDF 研究データあり 被引用文献10件 参考文献55件
  • Shinji Kanegawa
    Graduate School of Pharmaceutical Sciences, Kyushu University
  • Satoru Karasawa
    Graduate School of Pharmaceutical Sciences, Kyushu University
  • Motohiro Nakano
    Department of Applied Chemistry, Graduate School of Engineering, Osaka University
  • Noboru Koga
    Graduate School of Pharmaceutical Sciences, Kyushu University

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<jats:title>Abstract</jats:title> <jats:p>Three cobalt(II) complexes, [Co(X)2(4NOpy)4] (X = NCO−, NCS−, and Br−; 4NOpy = 4-(N-tert-butylaminoxyl)pyridine) were prepared, and their molecular structures were characterized by X-ray structure analysis. The molecular geometry of [Co(X)2(4NOpy)4] (X = NCO− and NCS−) is a compressed octahedron, in which the counter ions occupy the apical positions with short bond distances of 2.064–2.098 Å. In the crystalline state, from plots of χmol vs T and χ′mol vs T, [Co(NCO)2(4NOpy)4] and [Co(NCS)2(4NOpy)4] are antiferromagnets with TN = 4.5 and 15 K, respectively. In frozen solution, on the other hand, both complexes and [Co(Br)2(4NOpy)4] functioned as single-molecule magnets. The χ″mol vs T plot for [Co(Br)2(4NOpy)4] gave a effective activation barrier (Ueff) of 20 K for the reorientation of the spin. From the field dependence of magnetization at various temperatures below 5 K for [Co(X)2(4NOpy)4] (X = NCO−, NCS−, and Br−) the values of the zero-field splitting parameters, D/kB, were estimated to be −14, −9.7, and −4.5 K with S = 5/2, respectively. Theoretical studies based on the ligand-field theory model for [Co(NCO)2(4NOpy)4] gave an exchange coupling parameter, J/kB, of 29 K and a thermodynamic activation barrier, U, of 60 K.</jats:p>

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