Organic Counteranion Co-assembly Strategy for the Formation of γ‑Cyclodextrin-Containing Hybrid Frameworks

A class of γ-cyclodextrin-containing hybrid frameworks (CD-HFs) has been synthesized, employing γ-cyclodextrin (γ-CD) as the primary building blocks, along with 4-methoxysalicylate (4-MS–) anions as the secondary building blocks. CD-HFs are constructed through the synergistic exploitation of coordinative, electrostatic, and dispersive forces. The syntheses have been carried out using an organic counteranion co-assembly strategy, which allows for the introduction of 4-MS–, in place of inorganic OH–, into the cationic γ-CD-containing metal–organic frameworks (CD-MOFs). Although the packing arrangement of the γ-CD tori in the solid-state superstructure of CD-HFs is identical to that of the previously reported CD-MOFs, CD-HFs crystallize with lower symmetry and in the cuboid space group P43212when compared to CD-MOF-1, which has the cubic unit cell of I432 space groupon account of the chiral packing of the 4-MS– anions in the CD-HF superstructures. Importantly, CD-HFs have ultramicroporous apertures associated with the pore channels, a significant deviation from CD-MOF-1, as a consequence of the contribution from the 4-MS– anions, which serve as supramolecular baffles. In gas adsorption–desorption experiments, CD-HF-1 exhibits a Brunauer–Emmett–Teller (BET) surface area of 306 m2 g–1 for CO2 at 195 K, yet does not uptake N2 at 77 K, confirming the difference in porosity between CD-HF-1 and CD-MOF-1. Furthermore, the 4-MS– anions in CD-HF-1 can be exchanged with OH– anions, leading to an irreversible single-crystal to single-crystal transformation, with rearrangement of coordinated metal ions. Reversible transformations were also observed in CD-MOF-1 when OH– ions were exchanged for 4-MS– anions, with the space group changing from I432 to R32. This organic counteranion co-assembly strategy opens up new routes for the construction of hybrid frameworks, which are inaccessible by existing de novo MOF assembly methodologies.

一类以γ-环糊精（γ-cyclodextrin，γ-CD）为基本构筑单元、4-甲氧基水杨酸盐（4-methoxysalicylate，4-MS⁻）阴离子为次级构筑单元的杂化骨架（CD-HFs）已被成功合成。CD-HFs通过协同利用配位作用、静电作用与色散力构筑而成。本研究采用有机反阴离子共组装策略，成功将4-MS⁻替代无机OH⁻引入阳离子型含γ-CD的金属有机框架（CD-MOFs）中。尽管CD-HFs固态超结构中γ-CD环面的堆积排列与已报道的CD-MOFs一致，但由于4-MS⁻阴离子在CD-HF超结构中的手性堆积，相较于具有I432空间群立方晶胞的CD-MOF-1，CD-HFs的结晶对称性更低，其空间群为P43212。尤为重要的是，CD-HFs拥有与孔道相关的超微孔孔径，这与CD-MOF-1存在显著差异，其原因在于作为超分子挡板的4-MS⁻阴离子的贡献。在气体吸附-脱附实验中，CD-HF-1在195K下对CO₂的布鲁诺尔-埃米特-泰勒（Brunauer-Emmett-Teller，BET）比表面积为306 m²·g⁻¹，但在77K下不吸附N₂，这证实了CD-HF-1与CD-MOF-1在孔隙率上的差异。此外，CD-HF-1中的4-MS⁻阴离子可与OH⁻阴离子发生交换，伴随配位金属离子的重排，最终发生不可逆的单晶到单晶转变。当将OH⁻离子交换为4-MS⁻阴离子时，CD-MOF-1也发生了可逆转变，其空间群从I432转变为R32。该有机反阴离子共组装策略为构建现有de novo MOF组装方法无法实现的杂化骨架开辟了新路径。