New Hybrid Layered Molybdates Based on ²/_∞[Mo_nO_3n+1]^2– Units (n = 7, 9) with Systematic Organic–Inorganic Interfaces

Two new hybrid organic–inorganic molybdates based on layered ²/_∞[Mo_nO_3n+1]^2– blocks and organoammonium cations ⁺(Me_xH_3–xN)­(CH₂)₆(NH_3–xMe_x)⁺ (x = 0–1), namely, (H₃N­(CH₂)₆NH₃)­[Mo₇O₂₂]·H₂O (1) and (MeH₂N­(CH₂)₆NH₂Me)­[Mo₉O₂₈] (2), have been synthesized under hydrothermal conditions. The ²/_∞[Mo₉O₂₈]^2– unit in 2 is an unprecedented member of the ²/_∞[Mo_nO_3n+1]^2– family with the n value extended to 9. The structural filiation between the ²/_∞[Mo_nO_3n+1]^2– (n = 5, 7, 9) blocks is well established, and their structural similarity with the ²/_∞[MoO₃] slabs in α-MoO₃ is also discussed. Single-crystal X-ray analyses show that the ²/_∞[Mo_nO_3n+1]^2– layers in 1 and 2 are pillared in the three-dimensional networks by the organic cations with a similar connection at the organic–inorganic interface. In addition, a correlation between the topology of the ²/_∞[Mo_nO_3n+1]^2– blocks in 1 and 2 and the overall sizes of the associated organic cations is pointed out. Finally, the efficiency of Fourier transform Raman spectroscopy to easily discriminate the different ²/_∞[Mo_nO_3n+1]^2– blocks (n = 5, 7, 9) in hybrid organic–inorganic layered molybdate materials is clearly evidenced.