Magnetic properties of 1:4 complexes of CoIIX2 (X = NCO-, NCS-, and Br-) with 4-(N-tert-butylaminoxyl)pyridine.: Antiferromagnets in crystalline states and single-molecule magnets in frozen solutions
Magnetic properties of 1:4 complexes of CoIIX2 (X = NCO-, NCS-, and Br-) with 4-(N-tert-butylaminoxyl)pyridine.: Antiferromagnets in crystalline states and single-molecule magnets in frozen solutions
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DOI：
10.1246/bcsj.79.1372
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发表时间：
2006-09-15
影响因子：
4
通讯作者：
Koga, Noboru
中科院分区：
文献类型：
--
作者：
Kanegawa, Shinji;Karasawa, Satoru;Koga, Noboru
合成了3个钴（II）配合物[Co（X）（2）（4 NOpy）（4）]（X = NCO-、NCS-和Br-; 4 NOpy = 4-（N-叔丁基氨基氧基）吡啶），并通过X-射线衍射对其结构进行了表征。[Co（X）（2）（4 NOpy）（4）]（X = NCO-和NCS-）的分子几何构型为压缩八面体，其中抗衡离子占据顶点位置，短键距为2.064-2.098埃。在晶态下，由chi（mol）-T和chi '（mol）-T曲线可知，[Co（NCO）（2）（4 NOpy）（4）]和[Co（NCS）（2）（（4）NOpy）（4）]是反铁磁体，其T-N分别为4.5和15 K.另一方面，在冷冻溶液中，配合物和[Co（Br）（2）（4 NOpy）（4）]都起到单分子磁体的作用。[Co（Br）（2）（4 NOpy）（4）]的X”（mol）-T曲线给出了自旋重取向的有效激活势垒（U-eff）为20 K。根据[Co（X）（2）（4 NOpy）（4）]（X = NCO-，NCS-和Br-）在低于5 K的不同温度下的磁化强度的场依赖性，估算出零场分裂参数D/k（B）的值分别为-14，-9.7和-4.5 K（S = 5/2）。基于配位场理论模型对[Co（NCO）（2）（4 NOpy）（4）]进行了理论研究，得到交换耦合参数J/k（B）为29 K，热力学活化势垒U为60 K。
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 angstrom. In the crystalline state, from plots of chi(mol) vs T and chi'(mol) vs T, [Co(NCO)(2)(4NOpy)(4)] and [Co(NCS)(2)((4)NOpy)(4)] are antiferromagnets with T-N = 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 X"(mol) vs T plot for [Co(Br)(2)(4NOpy)(4)] gave a effective activation barrier (U-eff) 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/k(B), 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/k(B), of 29 K and a thermodynamic activation barrier, U, of 60 K.