Three new compounds [Ln(NMP)(4)(H2O)(4)][HxGeMo12O40].2NMP.3H(2)O (Ln = Ce-IV (1), Pr-IV (2), x = 0; Ln = Nd-III (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.