The reactions of M(2)MoO(4) . 2H(2)O Mo(CO)(6), and AlCl3 in propionic or acetic anhydride produce the aluminum(III)-molybdenum(IV) heterooctametallic clusters M(2)Al(2)[Mo3O4(O(2)CR)(8)](2) . nRCO(2)H (M = Na, K; R = Et. Me; n = 0, 1), in which the two incomplete cubane-type cluster units [Mo3O4(O(2)CR)(8)](4-) are bridged by two Al3+ ions to form a centrosymmetric cyclic structure. They decompose in HCl solution to produce isolated [Mo3O4](4+) units. In contrast to the sodium salts, the potassium salt is soluble in water and common organic solvents at room temperature.