Two polyoxometallate-based compounds, tris[1,1'-(butane-1,4-diyl)bis(1H-imidazol-3-ium)] bis[tetracosa-μ2-oxido-dodecaoxido-μ12-phosphato-dodecamolybdenum(VI)], (C10H16N4)3[PMo12O40]2, (I), and 1,1'-(butane-1,4-diyl)bis(1H-imidazol-3-ium) 1-[4-(1H-imidazol-1-yl)butyl]-1H-imidazol-3-ium tetracosa-μ2-oxido-dodecaoxido-μ12-phosphato-dodecamolybdenum(VI) dihydrate, (C10H16N4)(C10H15N4)[PMo12O40]·2H2O, (II), were synthesized by hydrothermal techniques at different pH values. The stoichiometric ratio between the polyoxometallate (POM) anions and organic cations is 2:3 in (I), with one of the cations lying on an inversion centre. The doubly protonated 1,1'-(butane-1,4-diyl)diimidazole (BIM) cations are linked to the [PMo12O40](3-) anions by hydrogen bonds to form a three-dimensional supramolecular network. The stoichiometric ratio of POM anions and organic cations is 1:2 in (II), and the anion is located about a centre of inversion. The partly protonated BIM cations and solvent water molecules form hydrogen bonds with the [PMo12O40](3-) anions, yielding a two-dimensional supramolecular layer. The different lattice architectures of (I) and (II) may be governed by the ratio between the POM anions and organic cations, which, in turn, is determined by the pH value.