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

The crystal structure of sodium pentamolybdyl tetradiphosphate Na-x(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 / 112/a(no. 15, setting 11),with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) angstrom, gamma = 90.641(9)degrees and a = 22.898(3), b = 23.056(2), c = 4.8551(2) angstrom, gamma = 90.82(1)degrees, for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90 degrees 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 Mo-2 and Mo-3 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. (C) 2007 Elsevier B.V. All fights reserved.