Role of Coordination Geometry on the Magnetic Relaxation Dynamics of Isomeric Five-Coordinate Low-Spin Co(II) Complexes.
Role of Coordination Geometry on the Magnetic Relaxation Dynamics of Isomeric Five-Coordinate Low-Spin Co(II) Complexes.
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DOI：
10.1021/acs.inorgchem.1c02881
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发表时间：
2021-12
影响因子：
4.6
通讯作者：
L. Spillecke;Shalini Tripathi;C. Koo;Arne Bahr;Abinash Swain;Rajashi Haldar;Mursaleem Ansari;J. Jasinski;G. Rajaraman;M. Shanmugam;R. Klingeler
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文献类型：
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作者：
L. Spillecke;Shalini Tripathi;C. Koo;Arne Bahr;Abinash Swain;Rajashi Haldar;Mursaleem Ansari;J. Jasinski;G. Rajaraman;M. Shanmugam;R. Klingeler
为了研究配位几何构型对磁化驰豫动力学的影响，合成了通式为[Co(DPPE)2Cl]SnCl3(DPPE=二苯基膦乙烷)的五配位低自旋钴(II)配合物的两个几何异构体，并对其结构进行了表征。其中一个异构体为四方锥体构型(Co-SP(1))，另一个异构体为三方双锥体构型(Co-TBP(2))。这两个建筑群在其他地方都已经有报道。这些复合体的自旋状态由详细的直流(DC)磁数据、X波段和高频EPR测量明确确定。对于S 1/2的体系，磁化强度的慢弛豫是很常见的。然而，1和2都表现出磁场诱导的磁化强度慢弛豫。特别是1在T=1.8K时的弛豫时间达到τ=35ms，这比未稀释的Co(II)低自旋单体的报道值要长得多。在文献2中，最大场致弛豫时间被抑制到τ=5ms。我们将这归因于g各向异性的变化，而g各向异性又与Co(II)离子周围配体的空间排列(即配位几何)相关。除了这些络合物的详细电子结构外，实验观察结果还得到了理论计算的进一步证实。
To investigate the influence of the coordination geometry on the magnetization relaxation dynamics, two geometric isomers of a five-coordinate low-spin Co(II) complex with the general molecular formula [Co(DPPE)2Cl]SnCl3 (DPPE = diphenylphosphinoethane) were synthesized and structurally characterized. While one isomer has a square pyramidal geometry (Co-SP (1)), the other isomer figures a trigonal bipyramidal geometry (Co-TBP (2)). Both complexes were already reported elsewhere. The spin state of these complexes is unambiguously determined by detailed direct current (dc) magnetic data, X-band, and high-frequency EPR measurements. Slow relaxation of magnetization is commonly observed for systems with S > 1/2. However, both 1 and 2 show field-induced slow relaxation of magnetization. Especially 1 shows relaxation times up to τ = 35 ms at T = 1.8 K, which is much longer than the reported values for undiluted Co(II) low-spin monomers. In 2, the maximal field-induced relaxation time is suppressed to τ = 5 ms. We attribute this to the change in g-anisotropy, which is, in turn, correlated to the spatial arrangement of ligands (i.e., coordination geometry) around the Co(II) ions. Besides the detailed electronic structure of these complexes, the experimental observations are further corroborated by theoretical calculations.