Chilton Nicholas F, Deacon Glen B, Gazukin Olga, Junk Peter C, Kersting Berthold, Langley Stuart K, Moubaraki Boujemaa, Murray Keith S, Schleife Frederik, Shome Mahasish, Turner David R, Walker Julia A
School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
Inorg Chem. 2014 Mar 3;53(5):2528-34. doi: 10.1021/ic402672m. Epub 2014 Feb 12.
Three complexes of the form [Ln(III)3(OQ)9] (Ln = Gd, Tb, Dy; OQ = 8-quinolinolate) have been synthesized and their magnetic properties studied. The trinuclear complexes adopt V-shaped geometries with three bridging 8-quinolinolate oxygen atoms between the central and peripheral eight-coordinate metal atoms. The magnetic properties of these three complexes differ greatly. Variable-temperature direct-current (dc) magnetic susceptibility measurements reveal that the gadolinium and terbium complexes display weak antiferromagnetic nearest-neighbor magnetic exchange interactions. This was quantified in the isotropic gadolinium case with an exchangecoupling parameter of J = -0.068(2) cm(-1). The dysprosium compound displays weak ferromagnetic exchange. Variable-frequency and -temperature alternating-current magnetic susceptibility measurements on the anisotropic cases reveal that the dysprosium complex displays single-molecule-magnet behavior, in zero dc field, with two distinct relaxation modes of differing time scales within the same molecule. Analysis of the data revealed anisotropy barriers of Ueff = 92 and 48 K for the two processes. The terbium complex, on the other hand, displays no such behavior in zero dc field, but upon application of a static dc field, slow magnetic relaxation can be observed. Ab initio and electrostatic calculations were used in an attempt to explain the origin of the experimentally observed slow relaxation of the magnetization for the dysprosium complex.
已合成了三种形式为[Ln(III)3(OQ)9]（Ln = Gd、Tb、Dy；OQ = 8 - 喹啉醇盐）的配合物，并对其磁性质进行了研究。三核配合物采用V形几何结构，在中心和外围的八配位金属原子之间有三个桥连的8 - 喹啉醇盐氧原子。这三种配合物的磁性质差异很大。变温直流（dc）磁化率测量表明，钆和铽配合物表现出弱的反铁磁最近邻磁交换相互作用。在各向同性的钆的情况下，用交换耦合参数J = -0.068(2) cm(-1)对其进行了量化。镝化合物表现出弱的铁磁交换。对各向异性情况进行的变频和变温交流磁化率测量表明，镝配合物在零直流场中表现出单分子磁体行为，在同一分子内有两个不同时间尺度的明显弛豫模式。对数据的分析揭示了这两个过程的有效各向异性势垒分别为Ueff = 92和48 K。另一方面，铽配合物在零直流场中没有这种行为，但在施加静态直流场时，可以观察到缓慢的磁弛豫。使用从头算和静电计算试图解释实验观察到的镝配合物磁化强度缓慢弛豫的起源。
