Thermodynamically metastable chain and stable layered Co(NCS)2 coordination polymers: thermodynamic relations and magnetic properties.
Thermodynamically metastable chain and stable layered Co(NCS)2 coordination polymers: thermodynamic relations and magnetic properties.
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DOI：
10.1039/d0dt03227a
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发表时间：
2020-10
影响因子：
4
通讯作者：
Aleksej Jochim;M. Rams;Michael Böhme;Magdalena Ceglarska;W. Plass;C. Näther
中科院分区：
文献类型：
--
作者：
Aleksej Jochim;M. Rams;Michael Böhme;Magdalena Ceglarska;W. Plass;C. Näther
Co（NCS）_2与4-溴吡啶反应生成了Co（NCS）_2（4-溴吡啶）_4·（CH_3CN）_0.67（1）、Co（NCS）_2（4-溴吡啶）_2（H_2O）_2（2）、Co（NCS）_2（4-溴吡啶）_2（CH_3OH）_2（3）和Co（NCS）_2（4-溴吡啶）_2（CH_3CN）_2（4）。在加热时，化合物2和4转化为具有组成Co（NCS）2（4-溴吡啶）2（5-I）的结晶产物，其也可以容易地从溶液中获得。在该化合物中，Co阳离子通过单个μ-1，3-桥硫氰酸根阴离子连接成层。3的热分解产生第二异构体（5-II），其是热力学亚稳的，并且也可以在动力学控制下从溶液合成。与5-I相反，Co阳离子通过阴离子配体对连接成线性链。5-I中的磁交换非常弱，但5-II中的磁交换强得多，并且沿沿着线性链具有铁磁性。在3.05 K时，5-II中达到AF有序，在变磁转变处观察到磁弛豫，其Arbellius势垒为17.1（3）cm-1。从头计算研究揭示了不同类型的磁各向异性存在于两个晶体学独立的Co中心5-II。
Reaction of Co(NCS)2 with 4-bromopyridine leads to the formation of discrete complexes with the composition Co(NCS)2(4-bromopyridine)4·(CH3CN)0.67 (1), Co(NCS)2(4-bromopyridine)2(H2O)2 (2), Co(NCS)2(4-bromopyridine)2(CH3OH)2 (3) and Co(NCS)2(4-bromopyridine)2(CH3CN)2 (4). Upon heating compounds 2 and 4 transform into a crystalline product with the composition Co(NCS)2(4-bromopyridine)2 (5-I) that also can easily be obtained from solution. In this compound, the Co cations are linked by single μ-1,3-bridging thiocyanate anions into layers. Thermal decomposition of 3 leads to a second isomer (5-II), which is thermodynamically metastable and can also be synthesized from solution under kinetic control. In contrast to 5-I, the Co cations are linked by pairs of anionic ligands into linear chains. The magnetic exchange is very weak in 5-I, but much stronger and ferromagnetic along the linear chains in 5-II. AF ordering in 5-II is reached at 3.05 K, and magnetic relaxation is observed at the metamagnetic transition with an Arrhenius barrier of 17.1(3) cm-1. Ab initio computational studies reveal a different type of magnetic anisotropy to be present in the two crystallographically - independent Co centers in 5-II.