Host–guest inclusion compounds with multistage reversible phase transitions are ideal materials for constructing molecular ferroelectrics. However, how to accurately design a molecular ferroelectric from a non-ferroelectric phase transition to a ferroelectric phase transition is still a huge challenge. Herein, we have successfully synthesized two high-temperature ferroelectrics [Hcta-(18-crown-6)]⁺[BF₄]⁻ (1) and [Hcta-(18-crown-6)]⁺[ClO₄]⁻ (2) (Hcta = protonated 3-cyclopentene amine). Compounds 1 and 2 crystallize in the ferroelectric space group Pca2₁. The phase transition mechanism of compound 1 can be attributed to the 2-fold disorder of the Hcta cation and the BF₄⁻ anion, resulting in the occurrence of two successive phase transitions to be a two-step NLO switch. Both clathrates exhibit clear ferroelectric phase transitions at about 403 and 394 K, respectively, which are significantly higher than those of BaTiO₃ (T_c = 393 K). The spontaneous polarization (P_s ) for 1 and 2 is ca. 5.7 μC cm⁻² and 4.7 μC cm⁻², respectively.

中文翻译：

---

具有非线性光学开关和大自发极化行为的异常高温主客体包合物基铁电体

具有多级可逆相变的主客体包合物是构建分子铁电体的理想材料。然而，如何准确地设计分子铁电体从非铁电相变到铁电相变仍然是一个巨大的挑战。在此，我们成功合成了两种高温铁电体[Hcta-(18-crown-6)] ⁺ [BF ₄ ] ^- ( 1 ) 和[Hcta-(18-crown-6)] ⁺ [ClO ₄ ] ^- ( 2 ) (Hcta = 质子化 3-环戊烯胺)。化合物1和2在铁电空间群Pca 2中结晶₁ . 化合物1的相变机制可归因于 Hcta 阳离子和 BF ₄ ^-阴离子的 2 倍无序，导致发生两个连续的相变，成为两步 NLO 开关。两种包合物分别在约 403 和 394 K 时表现出明显的铁电相变，明显高于 BaTiO ₃ ( T _c = 393 K)。1和2的自发极化 ( P _s )约为。分别为5.7 μC cm ^-2和 4.7 μC cm ^-2。