Histidinium-Driven Chirality Control of Self-Assembled Hybrid Molybdenum Oxyfluorides

Exploring macroscopic chiral materials with extended structures has become an important and fundamental topic in chemistry. To systematically control the chirality of novel organic–inorganic frameworks, histidinium-based cationic structure-directing agents containing specific chiral information are introduced. In this way, two chiral compounds, (l -hisH₂)MoO₂F₄]₃ ? H₂O ( L ) and (d -hisH₂)MoO₂F₄]₃ ? H₂O ( D ), and an achiral oxyfluoride, (l /d -hisH₂)MoO₂F₄ ( LD ) (his=histidine, C₆H₉N₃O₂) have been successfully self-assembled by a slow evaporation method. The structures of these compounds are composed of histidinium cations and distorted MoO₂F₄]^2? octahedra. Surprisingly, the histidinium cations not only control macroscopic chirality, but also induce O/F ordering in MoO₂F₄ octahedra through hydrogen-bonding interactions. Compounds L and D crystallize in the extremely rare polar space group P1, and exhibit positive second harmonic generation (SHG) signals attributable to a net moment originating from the MoO₂F₄ groups. Solid-state circular dichroism (CD) spectra indicate that the MoO₂F₄ units templated by histidinium cations are chirally aligned through ionic interactions. Crystallization processes influenced by the chirality of the reported materials are also discussed herein.