Crystal structure of Nax(MoO)5(P2O7)4 studied by synchrotron X-ray diffraction

The crystal structure of sodium pentamolybdyl tetradiphosphate Nax(MoO)5(P2O7)4 has been determined from synchrotron diffraction data collected at 293 K on two microcrystals. The compound crystallizes in a monoclinic space group I 1 1 2/a (no. 15, setting 11), with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) A, gamma = 90.641(9) deg and a = 22.898(3), b = 23.056(2), c = 4.8551(2) A, gamma = 90.82(1) deg , for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90 deg rotation around the c-axis. The structure closely resembles the previously reported Li-deintercalated Mo1.3OP2O7 [V.V. Lisnyak, N.V. Stus, P. Popovich, D.A. Stratiychuk, Ya. Filinchuk, V.M. Davydov, J. Alloys Compd. 360 (2003) 81-84]. Comparison of the two structures led us to conclude that the Mo2 and Mo3 clusters were erroneously identified in Mo1.3OP2O7. A revised structure of Mo1.3OP2O7 contains a fully occupied oxygen site instead of the 16% occupied Mo(2) site, thus the revised formulae for the Li-deintercalated compound is (MoO)5(P2O7)4. In both structures, the (MoO)5(P2O7)4 framework strongly resembles the one in the earlier reported Ag(MoO)5(P2O7)4, while the location of Na and Ag atoms differ.