In the reaction of MoO2Cl2 and MoO22Br2 with propionic anhydride, new complexes of molybdenum(V), and Mo4O6Br2(OCOC2H5)6, respectively, have been prepared. The crystal structure of the former was determined from single crystal diffractometer data and refined to the final R value of 0.046. The complex crystallizes in the monoclinic space group P2!n with cell dimensions a = 11.713(2) Å, b = 9.292(3) Å, c = 30.957(6) Å, f = 96.71(2)°, Z)caic = 1.963 g cm-3, Z = 4. The tetranuclear complex molecule contains four molybdenum atoms bridged through two oxo- oxygen atoms and six bidentate propionato-ligands. Two of the four molybdenum atoms form a Mo-Mo bond at 2.592(3) A
