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.
制备了三种
钴(II)配合物 [Co(X)2(4NOpy)4](X = NCO-、
NCS- 和 Br-;4NOpy = 4-(N-叔丁基
氨基氧基)
吡啶),并通过 X 射线结构分析鉴定了它们的分子结构。Co(X)2(4NOpy)4](X = NCO- 和
NCS-)的分子几何形状是一个压缩的八面体,其中反离子占据顶端位置,键距较短,为 2.064-2.098 Å。在结晶状态下,从 χmol vs T 和 χ′mol vs T 的曲线图来看,[Co(NCO)2(4NOpy)4] 和 [Co(
NCS)2(4NOpy)4] 是反
铁磁体,TN 分别为 4.5 和 15 K。另一方面,在冷冻溶液中,这两种配合物和[Co(Br)2(4NOpy)4]都起着单分子磁体的作用。根据[Co(Br)2(4NOpy)4]的χ″mol vs T 曲线,自旋重新定向的有效激活障碍(Ueff)为 20 K。根据[Co(X)2(4NOpy)4](X = NCO-、
NCS- 和 Br-)在 5 K 以下不同温度下磁化的磁场依赖性,估计零场分裂参数 D/kB 的值分别为 -14、-9.7 和 -4.5 K,S = 5/2。根据
配体-场理论模型对[Co(NCO)2(4NOpy)4]进行的理论研究得出,交换耦合参数 J/kB 为 29 K,热力学活化势垒 U 为 60 K。