Two new organic–inorganic hybrid compounds based on Keggin-type polyoxometalates and melaminium cations, namely (C3N6H7)3[PW12O40]·6H2O (1) and (C3N6H7)4[SiW12O40]·6H2O (2) have been synthesized at room temperature by a solvent diffusion method and characterized by IR spectroscopy, CHN analyses and single-crystal X-ray diffraction. Hybrid 1 consists of three melamonium cations per [PW12O40]3− unit with the hydration water molecules connected to each other via hydrogen bonding forming a 1D zigzag chain. In compound 2, [SiW12O40]4− polyanions and water molecules act as inorganic layers that are alternating with layers of monoprotonated organic melaminium cations.
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