Enhancing the Magnetic Anisotropy of Linear Cr(II) Chain Compounds Using Heavy Metal Substitutions
Enhancing the Magnetic Anisotropy of Linear Cr(II) Chain Compounds Using Heavy Metal Substitutions
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DOI：
10.1021/acs.inorgchem.5b02545
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发表时间：
2016-07-04
影响因子：
4.6
通讯作者：
Dalal, Naresh S.
中科院分区：
文献类型：
--
作者：
Christian, Jonathan H.;Brogden, David W.;Dalal, Naresh S.
本文用变温直流、交流磁力仪和高频EPR谱研究了三种线型三金属链状化合物Cr_2Cr（dpa）（4）Cl-2，1，Mo_2Cr（dpa）（4）Cl-2，2和W_2Cr（dpa）（4）Cl-2，3（dpa = 2，2 ′-dipyridylamido）的磁性。所有这三种化合物具有S = 2电子基态所产生的终端Cr 2+离子，表现出缓慢的磁弛豫下施加的磁场，证明了交流磁化率和磁化强度测量。缓慢的弛豫源于易轴磁各向异性的存在，这是由化合物的轴对称性支持，并已通过严格的高频EPR测量量化。当较重的离子被取代到三金属链中时，这些化合物中D的大小增加;因此，对于Cr2 Cr（dpa）（4）Cl-2，Mo 2Cr（dpa）（4）Cl-2和W2 Cr（dpa）（4）Cl-2，D分别为-1.640，-2.187和-3.617 cm（-1）。此外，W2 Cr（dpa）（4）Cl-2的D值是高自旋Cr 2+系统中迄今报道的最大值。虽然早期的研究已经证明，含有重原子的配体可以增强磁各向异性，这是第一次报告这种现象使用重金属原子作为“配体”。
Magnetic properties of the series of three linear, trimetallic chain compounds Cr2Cr(dpa)(4)Cl-2, 1, Mo2Cr(dpa)(4)Cl-2, 2, and W2Cr(dpa)(4)Cl-2, 3 (dpa = 2,2'-dipyridylamido), have been studied using variable-temperature dc and ac magnetometry and high-frequency EPR spectroscopy. All three compounds possess an S = 2 electronic ground state arising from the terminal Cr2+ ion, which exhibits slow magnetic relaxation under an applied magnetic field, as evidenced by ac magnetic susceptibility and magnetization measurements. The slow relaxation stems from the existence of an easy-axis magnetic anisotropy, which is bolstered by the axial symmetry of the compounds and has been quantified through rigorous high-frequency EPR measurements. The magnitude of D in these compounds increases when heavier ions are substituted into the trimetallic chain; thus D = -1.640, -2.187, and -3.617 cm(-1) for Cr2Cr(dpa)(4)Cl-2, Mo2Cr(dpa)(4)Cl-2, and W2Cr(dpa)(4)Cl-2, respectively. Additionally, the D value measured for W2Cr(dpa)(4)Cl-2 is the largest yet reported for a high-spin Cr2+ system. While earlier studies have demonstrated that ligands containing heavy atoms can enhance magnetic anisotropy, this is the first report of this phenomenon using heavy metal atoms as "ligands".