Evidence for single-chain magnet behavior in a MnIII-NiII chain designed with high spin magnetic units:: A route to high temperature metastable magnets
Evidence for single-chain magnet behavior in a MnIII-NiII chain designed with high spin magnetic units:: A route to high temperature metastable magnets
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DOI：
10.1021/ja0203115
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发表时间：
2002-10-30
影响因子：
15
通讯作者：
Coulon, C
中科院分区：
文献类型：
--
作者：
Clérac, R;Miyasaka, H;Coulon, C
本文报道了一种新的Mn-Ⅲ和Ni-Ⅱ杂金属链[Mn-2（saltmen）（2）Ni（pao）（2）（py）（2）]（ClO_4）（2）（1）（saltmen（2-）= N，N ′-（1，1，2，2-四甲基亚乙基）双水杨醛亚胺酸盐，pao（-）=吡啶-2-醛肟酸盐）的合成、晶体结构和磁性。通过X射线晶体学分析研究1的晶体结构：化合物1为单斜晶系，空间群C2/c（编号15），其中a = 21.140（3）埃，B = 15.975（1）埃，c = 18.6212（4）埃，β = 98.0586（4）度，V = 6226.5（7）埃（3），Z = 4。该化合物由两个片段组成，作为配位受体结构单元的面外二聚体[Mn-2（saltmen）（2）]（2+）和作为配位供体结构单元的中性单核单元[Ni（pao）（2）（py）（2）]，形成具有重复单元[-Mn-（O）（2）-Mn-ON-Ni-NO-]（n）的交替链。在晶体结构中，每个链被很好地分离，Mn和Ni离子之间的最小金属间距离为10.39埃，并且有机配体之间不存在链间π重叠。这些特征确保了链条的良好磁隔离。对1的多晶样品和取向单晶进行直流和交流磁性测量。在30 K以上，这种一维化合物的磁化率在平均场近似下被成功地描述为三聚体（（MnNiMn）-Ni-... - Mn-.）用（NiMnIII）-Mn-II.反铁磁相互作用（J = -21 K）通过铁磁（MnMnIII）-Mn-III.相互作用（J）。然而，平均场理论不能描述低于30 K的磁性行为，强调标题化合物的一维磁性特征。在5和15 K之间，在链方向上的磁化率拟合到一维伊辛模型，导致相同的J值。在3.5 K以下观察到磁滞回线，表明磁体型行为。在相同的温度范围内，交流和直流相结合的测量显示出一个缓慢的弛豫的磁化。这一结果表明，存在一个亚稳态没有磁性长程有序。这种材料是具有S-T = 3磁性单元的异金属链的第一个实验设计，显示出R. Glauber的Ising一维系统。这项工作开辟了新的视角，一维系统，以获得高温亚稳磁体相结合的高自旋磁单元，强大的单元间相互作用，和单轴各向异性。
We herein present the synthesis, crystal structure, and magnetic properties of a new heterometallic chain of Mn-III and Ni-II ions, [Mn-2(saltmen)(2)Ni(pao)(2)(py)(2)](ClO4)(2) (1) (saltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate) and pao(-) = pyridine-2-aldoximate). The crystal structure of 1 was investigated by X-ray crystallographic analysis: compound 1 crystallized in monoclinic, space group C2/c (No. 15) with a = 21.140(3) Angstrom, b = 15.975(1) Angstrom, c = 18.6212(4) Angstrom, beta = 98.0586(4)degrees, V = 6226.5(7) Angstrom(3), and Z = 4. This compound consists of two fragments, the out-of-plane dinner [Mn-2(saltmen)(2)](2+) as a coordination acceptor building block and the neutral mononuclear unit [Ni(pao)(2)(py)(2)] as a coordination donor building block, forming an alternating chain having the repeating unit [-Mn-(O)(2)-Mn-ON-Ni-NO-](n). In the crystal structure, each chain is well separated with a minimum intermetallic distance between Mn and Ni ions of 10.39 Angstrom and with the absence of interchain pi overlaps between organic ligands. These features ensure a good magnetic isolation of the chains. The dc and ac magnetic measurements were performed on both the polycrystalline sample and the aligned single crystals of 1. Above 30 K, the magnetic susceptibility of this one-dimensional compound was successfully described in a mean field approximation as an assembly of trimers ((MnNiMn)-Ni-...-Mn-...) with a (NiMnIII)-Mn-II... antiferromagnetic interaction (J = -21 K) connected through a ferromagnetic (MnMnIII)-Mn-III... interaction (J). However, the mean field theory fails to describe the magnetic behavior below 30 K emphasizing the one-dimensional magnetic character of the title compound. Between 5 and 15 K, the susceptibility in the chain direction was fitted to a one-dimensional Ising model leading to the same value of J. Hysteresis loops are observed below 3.5 K, indicating a magnet-type behavior. In the same range of temperature, combined ac and dc measurements show a slow relaxation of the magnetization. This result indicates the presence of a metastable state without magnetic long-range order. This material is the first experimental design of a heterometallic chain with S-T = 3 magnetic units showing a "single-chain magnet" behavior predicted in 1963 by R. J. Glauber for an Ising one-dimensional system. This work opens new perspectives for one-dimensional systems to obtain high temperature metastable magnets by combining high spin magnetic units, strong interunit interactions, and uniaxial anisotropy.