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.