Synthesis, Crystal Structure, and Photochromism of Novel Two-Dimensional Supramolecular Networks Based on Keggin-Type Polyoxoanion and Lanthanide Coordination Cations

Three new compounds [Ln(NMP)4(H2O)4][HxGeMo12O40]·2NMP·3H2O (Ln = CeIV (1), PrIV (2), x = 0; Ln = NdIII (3), x = 1; NMP = N-methyl-2-pyrrolidone) have been prepared in aqueous solution and characterized by elemental analyses, IR, UV−vis, and TG analyses. The single crystal X-ray diffraction shows that all three compounds are isostructural. In their structures, an interesting two-dimensional supramolecular network is constructed by the [GeMo12O40]4- anion and [Ln(NMP)4(H2O)4]3+/4+ cation building blocks via hydrogen-bonding interactions, exhibiting the porous structure. Upon irradiation with UV light, the crystals of 1−3 show photochromic behavior.