Two new heptamolybdates, one containing calcium and imidazole and the other with urea and ammonium cations, have been prepared. X-ray crystallographic studies of single crystals of both compounds have been carried out. In the mixture of calcium and imidazole [(Himi) 4 ][Ca(H 2 O) 6 (μ-O) 2 ][Mo 7 O 2 4 ].2(imi).3H 2 O (1), the calcium(II) cation is surrounded by six water molecules and two oxygen atoms from the polyanion, and bridges in trans position two [Mo 7 O 2 4 ] 6 - polyanions forming a linear composite with alternating Mo 7 O 2 4 and Ca(H 2 O) 6 units. The urea compound [CO(NH 2 ) 2 H] 3 (NH 4 ) 9 [Mo 7 O 2 4 ] 2 .5[CO(NH 2 ) 2 ].4H 2 O (2) presents [Mo 7 O 2 4 ] 6 - heptamolybdate anions bound by hydrogen bonds from NH 4 + , [CO(NH 2 )H] cations and H 2 O molecules. A new crystalline phase of a γ-octamolybdate containing pyrazole coordinatively bound to molybdenum has also been prepared [(Hpyr) 4 ][(pyr) 2 (Mo 8 O 2 6 )]CH 3 COCH 3 .2H 2 O (3). The structure has been solved by X-ray diffraction from a single crystal. The Mo N bond length is 2.262(3) 9. All compounds have been characterised by IR, 1 H NMR and thermal analysis.