Crystal packing effects on the magnetic slow relaxation of Tb(III)-nitronyl nitroxide radical cyclic dinuclear clusters.
Crystal packing effects on the magnetic slow relaxation of Tb(III)-nitronyl nitroxide radical cyclic dinuclear clusters.
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DOI：
10.1021/ic301394x
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发表时间：
2012-11
影响因子：
4.6
通讯作者：
Fabrice Pointillart;Kévin Bernot;G. Poneti;R. Sessoli
中科院分区：
文献类型：
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作者：
Fabrice Pointillart;Kévin Bernot;G. Poneti;R. Sessoli
合成了四个式为[Ln(HfAc)3(NITPhPO(OEt)2)]2(Ln(III)=Gd(1)，Tb(2A和2B)，Dy(3)和NITPhPO(OEt)2=4‘-[2-(1-oxyl-3-4，4，5，5-tetramethylimidazoline)phenyl]diethoxylphosphine氧化物的稀土硝基氮氧化物自由基环分子簇。它们的X射线结构已被解决，并突出了两种不同的晶体堆积。对于Tb(III)衍生物的特殊情况，两者都可以得到。在A中，分子被很好地隔离，而在2B中，N-O基团之间的接触很短。对Gd(III)衍生物(1)的静态磁学研究表明，稀土元素与自由基是铁磁耦合的(J=3.46±0.04 cm(-1))。动态磁学研究表明，化合物2A和2B均表现出单分子磁体行为。通过对它们磁行为的比较，发现晶体堆积对观察到SMM行为的温度范围有重要影响。在绝缘良好的基于Tb(III)的衍生物(2A)的情况下，SMM行为在更高的温度和更低的频率下被观察到，而不是在分子(2B)之间呈现紧密堆积的情况下。只有在外加磁场(0.2T)下才能进行比较，其中Δ分别为27.5(6)和21.0(5)K，τ分别为2.64(25)×10(-9)和1.76(20)×10(-9)S。
Four lanthanide-based nitronyl nitroxide radical cyclic molecular clusters of formula [Ln(hfac)3(NITPhPO(OEt)2)]2 (Ln(III) = Gd (1), Tb (2A and 2B), and Dy (3) and NITPhPO(OEt)2 = 4'-[2-(1-oxyl-3-4,4,5,5-tetramethylimidazoline)phenyl]diethoxylphosphine oxide) have been synthesized. Their X-ray structures have been solved and highlight two different crystal packings. For the particular case of the Tb(III) derivative, both of them can be obtained. In 2A, the molecules are well-isolated, while 2B shows short contacts between N-O radical groups. Static magnetic studies on the Gd(III) derivative (1) demonstrate that lanthanides and radicals are ferromagnetically coupled (J = 3.46 ± 0.04 cm(-1)). Dynamic magnetic studies show that both compounds 2A and 2B exhibit single molecule magnet behavior. A comparison of their magnetic behaviors highlights that the crystal packing has a crucial influence on the temperature range in which the SMM behavior is observed. In the case of the well-insulated Tb(III)-based derivative (2A), the SMM behavior is observed at higher temperatures and lower frequencies than for the one that presents close-packing between the molecules (2B). Comparisons are then possible only under an applied external magnetic field (0.2 T) with Δ = 27.5(6) and 21.0(5) K and τ0 = 2.64(25) × 10(-9) and 1.76(20) × 10(-9) s for 2A and 2B, respectively.