Structural and Functional Modulation of Five 4‑Cyanopyridinium Iodoargentates Built Up from Cubane-like Ag₄I₄ Nodes

Five iodoargentate hybrids, {[MC]­[Ag2I3]}n (1), {[EC]­[Ag2I3]}n (2), {[PC]2[Ag4I6]}n (3), {[BC]2[Ag4I6]}n (4), and {[IPC]2[Ag4I6]}n (5) (MC+ = N-methyl-4-cyanopyridinium, EC+ = N-ethyl-4-cyanopyridinium, PC+ = N-propyl-4-cyanopyridinium, BC+ = N-butyl-4-cyanopyridinium, and IPC+ = N-isopentyl-4-cyanopyridinium), have been solvothermally synthesized. Built up from μ-I bridging cubane-like Ag4I4 nodes, 1 and 2 present similar two-dimensional grid-like layers with the MC+ and EC+ cations located at the apertures of inorganic layers and interlayer space, while 3, 4, and 5 possess three-dimensional open frameworks with the PC+, BC+, and IPC+ cations intercalated in the channels. 1–5 exhibit reducing band gaps with respect to the bulk β-AgI and interesting low temperature reversible thermochromism, which can be ascribed to the temperature effects directly on the population of intermolecular charge transfer. Variations in structure and property reveal delicate modulating effect of N-alkyl-4-cyanopyridinium cations and flexibility of iodoargentate frameworks.本研究通过溶剂热法合成了五种碘银酸根（iodoargentate）杂化物，其结构式分别为{[MC]­[Ag₂I₃]}ₙ（1）、{[EC]­[Ag₂I₃]}ₙ（2）、{[PC]₂[Ag₄I₆]}ₙ（3）、{[BC]₂[Ag₄I₆]}ₙ（4）与{[IPC]₂[Ag₄I₆]}ₙ（5）。其中，MC⁺为N-甲基-4-氰基吡啶鎓阳离子，EC⁺为N-乙基-4-氰基吡啶鎓阳离子，PC⁺为N-丙基-4-氰基吡啶鎓阳离子，BC⁺为N-丁基-4-氰基吡啶鎓阳离子，IPC⁺为N-异戊基-4-氰基吡啶鎓阳离子。化合物1与2由μ-碘桥联的类立方烷型Ag₄I₄节点构筑，二者均呈现相似的二维网格状无机层结构，MC⁺与EC⁺阳离子分别位于无机层的孔道及层间空间内；而化合物3、4、5则拥有三维开放骨架结构，PC⁺、BC⁺与IPC⁺阳离子插居于其孔道之中。相较于本体β-碘化银（β-AgI），化合物1~5均展现出更窄的带隙，同时呈现出有趣的低温可逆热致变色现象，该性质可归因于温度对分子间电荷转移布居数的直接调控作用。结构与性能的变化揭示了N-烷基-4-氰基吡啶鎓阳离子对体系的精细调控效应，以及碘银酸根骨架的结构柔性。