A Mixed-Valent Molybdenotungsten Monophosphate with a Tunnel Structure: Nax(Mo, W)2O3(PO4)2

Abstract A mixed-valent molybdenotungstophosphate, Nax(Mo, W)2O3(PO4)2 (x ∼ 0.75) has been isolated for the first time. It crystallizes in the space group P 21/m with a = 7.200(1) A, b = 6.369(1) A, c = 9.123(1) A, and β = 106.29(1)°. Its structure consists of M2PO13 units built up of two M O6 octahedra (M = Mo, W) and one PO4 tetrahedron sharing their apices as already observed in several molybdenum phosphates. These units share their apices with PO4 tetrahedra forming [M2P2O15]∞ chains running along c. The host lattice [(Mo, W)2P2O11]∞ can be described by the assemblage of such chains or by the assemblage of [MPO8]∞ chains running along b , in which one PO4 tetrahedron alternates with one MO6 octahedron. The tridimensional framework [Mo, WP2O11]∞ delimits tunnels running along b, occupied by sodium with two kinds of coordination, 6 and 5. The distribution of the different species, in the octahedral sites according to the formulation Na0.75(MoVI0.42WVI0.58)M1 (MoV0.75WVI0.25)2O3(PO4)2, is discussed.