The construction of metal-organic frameworks (MOFs) has been an area of rapid growth in recent years, because of their structure diversity and potential applications as functional materials [1]. Polyoxometalates (POMs), as early transition metal clusters, have many properties that make them attractive for applications in catalysis, medicine and material science [2]. Hence, stabilization and immobilization of POMs through the formation of POMs containing MOFs is a remarkable approach for constructing multifunctional materials [3]. In this work an inorganic–organic hybrid compound based on one-electron-reduced Keggin polyanions and 3D lanthanide-organic coordination polymer; [La(H2O)4(pdc)]4 [PMo11VIMoVO40] · H2O(1) (pdc= pyridine-2,6-dicarboxylate), has been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, X-ray diffraction. X-ray crystallography reveals that the structure of 1 is constructed from of a noncoordinated [PMo11VIMoVO40]4- anion, four [La (H2O) 4(pdc)] + cations, and one crystalline water molecules. Each La3+ cation is coordinated in a distorted-square-anti- prismatic geometry by four water ligands, four oxygen atoms from three independent pdc ligands and one nitrogen atom from a pdc ligand. Four nine-coordinated La3+ ions are linked by carboxylate groups of four pdc ligands to form a tetranuclear cyclic unit {[La(H2O)4(pdc)]4}4+. Two tetranuclear cyclic units chelate one [PMo11VIMoVO40]4- ion through O–H---O hydrogen bonding. In addition, an octanuclear metallamacrocycle composed of La8 (pdc) 8 also can be abstracted from the topology. Thus, a 3D lanthanide-organic cationic architecture is built up from the tetranuclear cyclic units and octanuclear metallamacrocycles.

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