New Hybrid Layered Molybdates Based on 2/∞[MonO3n+1]2– Units (n = 7, 9) with Systematic Organic–Inorganic Interfaces

Two new hybrid organic–inorganic molybdates based on layered 2/∞[MonO3n+1]2– blocks and organoammonium cations +(MexH3–xN)­(CH2)6(NH3–xMex)+ (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/∞[MonO3n+1]2– family with the n value extended to 9. The structural filiation between the 2/∞[MonO3n+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/∞[MonO3n+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/∞[MonO3n+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/∞[MonO3n+1]2– blocks (n = 5, 7, 9) in hybrid organic–inorganic layered molybdate materials is clearly evidenced.