Open-framework polar compounds:: Synthesis and characterization of rare-earth polyoxometalates (C6NO2H5)2[Ln(H2O)5(CrMo6H6O24)•0.5H2O (Ln = Ce and La)

Two unprecedented open-framework polar compounds (C6NO2H5)(2)[Ln(H2O)(5)(CrMo6H6O24)]center dot 0.5H(2)O [Ln = Ce (1), La (2); C6NO2H5 = pyridine-3-carboxylic acid], constructed from Anderson-type polyoxo anions and rare-earth cations, have been synthesized for the first time and characterized by elemental analysis, IR and Raman spectroscopy, TG analysis, and single-crystal X-ray diffraction. Both compounds crystallize in the polar space group Pmn2(1) and are made up of [CrMo6H6O24](3-) polyoxo anions linked by rare-earth cations to form a fascinating 3D open framework with guest pyridine-3-carboxylic acid molecules and free water molecules residing in the channels. To the best of our knowledge, this represents the first example of an open-framework polar compound constructed from rare-earth polyoxometalates. The magnetic properties of compound 1 have been studied by measuring its magnetic susceptibility in the temperature range 2.0-300.0 K, indicating the existence of antiferromagnetic interactions. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).