Cyclic Single-Molecule Magnets: From Even-Numbered Hexanuclear to Odd-Numbered Heptanuclear Dysprosium Clusters

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• 作者：Haiquan Tian ; Song-Song Bao and Li-Min Zheng
• 刊名：European Journal of Inorganic Chemistry
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：2016
• 期：19
• 页码：3184-3190
• 全文大小：1712K
• ISSN：1099-0682c

文摘

An ingenious self-assembly method has been employed to achieve noncentered cyclic metal cages by integrating single and double pyrazinyl hydrazone ligands in the presence of an organo phosphonic acid. An even-numbered hexanuclear and an odd-numbered heptanuclear dysprosium(III) cluster, namely [Dy₆(spch)₆(O₃PC₁₀H₇)₂(pyra)₂(MeOH)(H₂O)]·8.5H₂O [1, H₂spch = (E)-N′-(2-hydroxybenzylidene)pyrazine-2-carbohydrazide, pyra = pyrazine-2-carboxylate] and [Dy₇(eddc)₂(spch)₂(O₃PC₁₀H₇)₄(OAc)₅(MeOH)₄]·4MeOH [2, H₂eddc = (E,E)-N′,N′′-(ethane-1,2-diylidene)bis(pyrazine-2-carbohydrazide)] have been synthesized successfully. Single-crystal X-ray diffraction analysis revealed that compound 1 is composed of six identical [Dy₂(spch)]⁴⁺ building blocks containing a single pyrazinyl hydrazone ligand of spch^2– welded to each other to form a hexanuclear ring, whereas compound 2 possesses an enlarged skeleton with a heptanuclear ring made up of two [Dy₃(eddc)]⁷⁺ and two [Dy₂(spch)]⁴⁺ building blocks by virtue of the inclusion in the synthesis of double pyrazinyl hydrazone ligand eddc^2–. Compounds 1 and 2 exhibit drastically distinct dynamic magnetic properties. Compound 1 shows a complex slow relaxation of the magnetization with two types of temperature dependence with energy barriers (U_eff) of 4.7 and 20.3 K and pre-exponential factors (τ₀) of 9.1 × 10^–5 and 2.6 × 10^–6 s for the low- and high-temperature regimes, respectively, whereas compound 2 exhibits a two-step relaxation process (U_eff⁽¹⁾: 45.1 K, τ₀⁽¹⁾: 4.4 × 10^–7 s; U_eff⁽²⁾: 48.7, τ₀⁽²⁾: 2.7 × 10^–8 s) in the out-of-phase alternating current signals.