A Mononuclear Dysprosium Complex Featuring Single-Molecule-Magnet Behavior
A Mononuclear Dysprosium Complex Featuring Single-Molecule-Magnet Behavior
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具有单分子磁体行为的单核镝配合物
DOI：
10.1002/anie.201004027
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Gao, Song
中科院分区：
文献类型：
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作者：
Jiang, Shang-Da;Wang, Bing-Wu;Gao, Song
单分子磁体（SMM）[1]由于其量子隧穿和慢弛豫而受到广泛关注。[2]当分子具有单轴磁各向异性的大自旋态，即负的零场分裂参数D时，可以观察到这些行为。除了大的基态外，控制磁各向异性对提高SMM的能垒和阻断温度至关重要。[3]理解决定团簇的各向异性或零场分裂性质的条件也是非常复杂的。[4]因此，只包含一个自旋载流子的SMM由于简化了对局域各向异性和自旋的分析而引起了极大的兴趣。最近，观察到一些具有孤立的3d [5]或4f [6]金属离子的分子显示出直流（dc）场诱导的缓慢磁弛豫。研究表明，这种依赖于直流场的弛豫现象是热激活的，直流场对快量子隧穿的猝灭可以引起慢弛豫。然而，正如Benelli和Gatteschi所评论的那样，这是一种意想不到的和令人困惑的行为，其潜在的机制仍然不清楚。石川等人报道了酞菁（Pc）双层阴离子配合物[Pc 2Ln]与单个TbIII或DyIII离子的络合物在没有直流场的情况下显示出缓慢的弛豫。[8]多金属氧酸盐体系[ErW_（10）O_（36）]_（9-x）中的单个Er ~（3+）离子在零静磁场下表现出类似的弛豫行为。[9]Rinehart和Long报道的第一个单锕系元素配合物[U（Ph 2BPz 2）3]（含有UIII离子; Ph 2BPz 2 =二苯基双（吡唑基硼酸盐））显示出类似的缓慢弛豫。[10]由于这些配合物的单离子特征，它们可以被称为“单离子磁体”。在这些配合物中，具有高阶单轴Cn（n> 2;对于Ref. [8，9]，对于参考文献，n= 3。[10])将（2 J + 1）简并基态分裂成新的子能级，这产生单轴各向异性，从而产生更高的弛豫能垒。[8b]DyIII离子具有Kramers基态6 H15/2，在合适的配体场对称性和强度下，是用于构建SMM的有吸引力的顺磁源。此外，在已报道的SMM中，其中一些是含有DyIII的簇：Dy 2，[11] Dy 3，[12] Dy 4，[13] Dy 5，[14]含有DyIII的链，[15]和数十个含有DyIII的3d-4f簇。[16]所有三种报告的单离子磁体[8]都具有定义局部对称性的高阶单轴。遵循这一线索，我们合成了一系列单核Ln III化合物，其局部对称性接近D4 d。晶体分析表明，同晶配合物由中性单核[Ln（acac）3（H2O）2]配合物（Ln= Dy、Ho、Er，acac=乙酰丙酮）以及未配位的水分子和未配位的乙醇分子组成（图1a）。在DyIII配合物中，Dy 3+被8个氧原子配位，Dy 3 + O键为2.311-2.434，其中6个来自乙酰丙酮配体，2个来自配位水分子。八个氧原子形成一个近似正方形的反棱柱配位多面体，DyIII的局部对称性接近D4 d（图1b）。实际上，类似的镧系acac络合物在1968年首次报道[17]，但是未配位的水和
Single-molecule magnets (SMMs)[1] have received much attention owing to their quantum tunneling and slow relaxation.[2] These behaviors can be observed when the molecule has large ground spin state with a uniaxial magnetic anisotropy, namely negative zero-field splitting (ZFS) parameter D. Besides a large ground state, to increase the SMMs energy barrier and blocking temperature, it is of fundamental importance to control the magnetic anisotropy.[3] It is also of great complexity to understand the conditions that determine the anisotropy or zero-field splitting properties for a cluster.[4] As a result, SMMs containing only one spin carrier are of great interest because of the simplification in the analysis of local anisotropy and ZFS. Recently, some molecules with isolated 3d [5] or 4f [6] metal ions were observed to show a direct-current (dc) field-induced slow magnetic relaxation. Studies show that this kind of dc-field-dependent relaxation phenomenon is thermally activated, and the quench of fast quantum tunneling by the dc field could give rise to the slow relaxation. However, as commented by Benelli and Gatteschi,[7] it is an unexpected and puzzling behavior, and the underlying mechanism is still unclear. Ishikawa et al. reported that the phthalocyanine (Pc) double-decker anion complexes [Pc2Ln] À with a single TbIII or DyIII ion show slow relaxation without a dc field.[8] A single ErIII ion in the polyoxometallate system [ErW10O36] 9À showed similar relaxation behavior in zero static magnetic field.[9] The first single-actinide complex [U (Ph2BPz2) 3](containing the UIII ion; Ph2BPz2= diphenylbis (pyrazolylborate)) reported by Rinehart and Long shows a similar slow relaxation.[10] Owing to the single-ion features, these complexes could be called “single-ion magnets”. In these complexes, ligand fields with a high-order single axis Cn (n> 2; n= 4 for Ref.[8, 9] and n= 3 for Ref.[10]) split the (2J+ 1) degenerate ground states into new sublevels, which produces a uniaxial anisotropy, thus giving rise to a higher energy barrier for relaxation.[8b] The DyIII ion, which possesses a Kramers ground state of 6H15/2, is an appealing paramagnetic source for the construction of SMMs in a suitable ligand-field symmetry and strength. Moreover, among reported SMMs, some of them are clusters containing DyIII: Dy2,[11] Dy3,[12] Dy4,[13] Dy5,[14] DyIII-containing chain,[15] and tens of DyIII-containing 3d–4f clusters.[16]All three reported types of single-ion magnets [8] are found with a high-order single axis defining the local symmetry. Pursuing this clue, we synthesized a series of mononuclear LnIII compounds with a local symmetry close to D4d. Crystal analysis shows that the isomorphous complexes consist of a neutral mononuclear [Ln (acac) 3 (H2O) 2] complex (Ln= Dy, Ho, Er, acac= acetylacetonate) together with an uncoordinated water molecule and an uncoordinated ethanol molecule (Figure 1a). In the DyIII complex, Dy3+ is coordinated by eight oxygen atoms with DyÀO bonds of 2.311–2.434, six of which come from the acetylacetonate ligand and two from coordinated water molecules. The eight oxygen atoms form an approximately square-antiprismatic coordination polyhedron, and the local symmetry of DyIII is nearly D4d (Figure 1b). Actually, a similar lanthanide acac complex was firstly reported in 1968,[17] but the uncoordinated water and