Layered and molecular-structural control in polyoxomolybdate hybrid crystals by surfactant chain length

• Polyoxomolybdate-surfactant hybrid crystals were synthesized as single crystals.
• Single-tailed alkyltrimethylammonium cations were employed as surfactant.
• The crystals consisted of alternate stacking of octamolybdate and surfactant layers.
• The layered distance became longer with an increase in alkyl chain length.
• The octamolybdate molecular structure depended on the alkyl chain length.

Polyoxomolybdate-surfactant hybrid layered crystals were synthesized by using single-tailed alkyltrimethylammonium ([CnH2n+1N(CH3)3]+ (Cn), n = 8, 10, 12, 14, 16, and 18) cations. The crystal structures consisted of alternate stacking of octamolybdate ([Mo8O26]4−, Mo8) anionic layers and surfactant cationic layers. The layered distance of the hybrid crystals became longer from 18.5 Å to 26.5 Å with an increase in alkyl chain length. Interestingly, the molecular structures of Mo8, which has several isomers, depended on the alkyl chain length of the employed surfactants. Shorter surfactant (C8 and C10) formed hybrid crystals containing β-type Mo8 isomer, while surfactant with longer alkyl chain (C12, C14, C16, and C18) gave crystals containing δ-type Mo8 isomer. This structural controllability will lead to the precise functional control in the polyoxomolybdate-surfactant hybrid layered crystals.