The hydrothermal synthesis of two new inorganic-organic hybrid materials in which PDA (PDA = 1,10-phenanthroline-2,9-dicarboxylate) is connected to a well-defined Keggin-type polyoxometalate anion (POM) and a Ln(III) cation (POM = [SiW12O40]4-; Ln = Eu3+ (1), Er3+ (2)), are reported. These hybrids are characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction. Single-crystal X-ray analysis reveals that both compounds have been assembled by hydrogen bonding and anion-π interactions among POM, PDA and lattice water units into a three-dimensional (3D) supramolecular structure. Compound 1 is composed of two different cationic layers of Eu(III) clusters with the POMs located in cavities that are created by the Eu-PDA groups. Compound 2 consists of [SiW12O40]4-Keggin-type POMs, where a single {W3O13} triad is decorated by a trinuclear Er(III)-complex.

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