Cu(hfac)2 Complexes with Nitronyl Ketones Structurally Mimicking Nitronyl Nitroxides in Breathing Crystals
Cu(hfac)2 Complexes with Nitronyl Ketones Structurally Mimicking Nitronyl Nitroxides in Breathing Crystals
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Cu(hfac)2 与硝硝基酮的配合物在结构上模仿呼吸晶体中的硝基氮氧化物
DOI：
10.1071/ch14422
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发表时间：
2015
影响因子：
1.1
通讯作者：
V. Ovcharenko
中科院分区：
文献类型：
--
作者：
S. Vasilevsky;E. Tretyakov;O. Usov;Yu. N. Molin;S. Fokin;Yuri G. Shwedenkov;V. Ikorskii;G. Romanenko;R. Sagdeev;V. Ovcharenko
基于Cu（hfac）2（hfac =六氟乙酰丙酮）与硝酰基氮氧化物的聚合物链复合物的呼吸晶体代表了一种新型的分子磁传感器，其表现出热和光诱导的自旋团簇Cu <$（O <$N<）n中的结构重排，并伴有磁异常。为了阐明重排的驱动力，确定了在呼吸晶体中合成空间位阻4-氧代-3，4-二氢-2H-吡咯-N-氧化物（硝酰基酮）的方法，该方法在结构上模仿硝酰基氮氧化物。该方法采用钯催化的3，3，4-三甲基-4-硝基戊酸氯与4-甲锡烷基吡唑的交叉偶联，导致硝基酮的形成，随后软还原成羟胺，然后进行自引发的环化成相应的硝酮。后者的自由基氧化最终产生目标硝酮。硝酮的X-射线衍射分析证实，它们的结构特征接近相应的硝酰基氮氧化物。此外，在与Cu（hfac）2反应时，抗磁性硝酰基酮形成具有“头到尾”基序的聚合物链复合物，其结构类似于含有顺磁性硝酰基氮氧化物的类似物。最后，已经发现与硝酮的配合物之一确实表现出类似于其铜-氮氧化物类似物的纯结构相变，但同时它没有表现出呼吸晶体的磁结构转变特征的任何迹象，其中配位单元CuNO 4（O N<）中的Jahn-Teller轴翻转。这一观察强烈证实了铜和氮氧化合物自旋之间的交换相互作用对于呼吸晶体中磁结构异常起源的关键作用。
Breathing crystals based on polymer-chain complexes of Cu(hfac)2 (hfac = hexafluoroacetylacetonate) with nitronyl nitroxides represent a new type of molecular magnetic sensors, exhibiting thermally and light-induced structural rearrangements in the spin clusters Cu ← (O∸N<)n accompanied by magnetic anomalies. To shed light on the driving forces of the rearrangements a method for the synthesis of sterically hindered 4-oxo-3,4-dihydro-2H-pyrrole-N-oxides (nitronyl ketones) structurally mimicking nitronyl nitroxides in breathing crystals has been determined. This method employs palladium-catalyzed cross-coupling of 3,3,4-trimethyl-4-nitropentanoic acid chloride with 4-stannylpyrazoles, leading to the formation of nitroketones followed by soft reduction into hydroxylamines, that then undergo self-initiated cyclization into the corresponding nitrones. The radical oxidation of the latter finally yields the target nitronyl ketones. An X-ray diffraction analysis of the nitronyl ketones confirms that their structural characteristics are close to those of the corresponding nitronyl nitroxides. Moreover, upon reaction with Cu(hfac)2, diamagnetic nitronyl ketones form polymer-chain complexes with a ‘head-to-tail’ motif and a structure similar to their analogues containing paramagnetic nitronyl nitroxides. Finally, it has been found that one of the complexes with nitronyl ketones does manifest a purely structural phase transition similar to its copper-nitroxide analogue, but at the same time it does not manifest any signs of a magneto-structural transition characteristic for breathing crystals where a Jahn–Teller axis in the coordination units CuNO4(O∸N<) is flipped. This observation strongly confirms the crucial role of the exchange interactions between spins of copper and nitroxide for the origin of magneto-structural anomalies in breathing crystals.