Exploration of Neutral Radical Systems Based on Oxophenalenoxyl as New Spin Source

新型稳定的有机中性自由基的合成以及对具有高度离域未成对电子的π电子体系的理解在新型有趣的有机分子基磁性材料的分子设计中起着至关重要的作用。6-氧代苯并萘氧基衍生物最初是基于苯并萘体系设计的，并且显示出足够高的持久性以在空气中处理。有趣的是，这个中性π-自由基系统被发现是独特的，表现出类似于母体phenalenyl系统的“极端自旋离域和高度自旋极化性质”，而自旋密度分布的拓扑结构与phenalenyl系统形成鲜明对比。6-oxophenalenoxyl衍生物电子自旋结构的这些显著特征使我们能够讨论π共轭单价自由基体系中自旋密度分布的拓扑对称性控制，这种控制源于Phenalenyl骨架上两个氧原子的连接性。在制备6-氧代苯烯氧基体系3-和4-氧代苯烯氧基拓扑异构体的基础上，阐明了这一新概念并进行了实验验证。此外，我们还成功地测定了这些oxophenalenoxyl衍生物的X-射线晶体结构，并证明了用于基于苯并萘基的中性π-自由基的大分子间磁交换相互作用的可行的晶体工程。

Syntheses of novel stable organic neutral radicals and understanding inherent in π-electronic systems with highly delocalized unpaired electrons play a crucial role in the molecular designs for novel intriguing organic molecule-based magnetic materials. 6-Oxophenalenoxyl derivatives were originally designed on the basis of the phenalenyl system, and showed high persistency enough to handle in air. Interestingly, this neutral π-radical system found to be unique in exhibiting both an "extremely spin-delocalized and highly spin-polarized nature" similar to that of the parent phenalenyl system, while the topology of the spin density distribution sharply contrasted with that of the phenalenyl system. These salient features in the electronic spin structures of 6-oxophenalenoxyl derivative enable us to discuss topological-symmetry control in spin density distribution in π-conjugated monoradical systems originating from the connectivities of the two oxygen atoms on the phenalenyl skeleton. This new concept was elucidated and exemplified experimentally on the basis of the preparation of topological isomers of 6-oxophenalenoxyl system, 3-and 4-oxophenalenoxyls. Furthermore, we have succeeded in the determinations of X-ray crystal structures of these oxophenalenoxyl derivatives, and demonstrated feasible crystal engineering for large intermolecular magnetic exchange interactions of phenalenyl-based neutral π-radicals.