Abstract
Two unprecedented open‐framework polar compounds (C~6~NO~2~H~5~)~2~[Ln(H~2~O)~5~(CrMo~6~H~6~O~24~)]·0.5H~2~O [Ln = Ce (1), La (2); C~6~NO~2~H~5~ = 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 __Pmn__2~1~ and are made up of [CrMo~6~H~6~O~24~]^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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)