Crystal Packing Effects on the Magnetic Slow Relaxation of Tb(III)-Nitronyl Nitroxide Radical Cyclic Dinuclear Clusters

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• 作者：Fabrice Pointillart ; Kevin Bernot ; Giordano Poneti ; Roberta Sessoli
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：November 19, 2012
• 年：2012
• 卷：51
• 期：22
• 页码：12218-12229
• 全文大小：680K
• 年卷期：v.51,no.22(November 19, 2012)
• ISSN：1520-510X

文摘

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鈥?[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鈥揙 radical groups. Static magnetic studies on the Gd^III derivative (1) demonstrate that lanthanides and radicals are ferromagnetically coupled (J = 3.46 卤 0.04 cm^鈥?). 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 螖 = 27.5(6) and 21.0(5) K and 蟿₀ = 2.64(25) 脳 10^鈥? and 1.76(20) 脳 10^鈥? s for 2A and 2B, respectively.