Two novel Mo(V) and Mo(V)/Mo(VI) barium phosphates with a tunnel structure: β-Ba(MoO)2(P2O7)2, and Ba(MoO)2O(P2O7)PO4

Two new Mo(V) and Mo(V)/Mo(VI) phosphates, β-Ba(MoO)2(P2O7)2 and Ba(MoO)2O(P2O7)PO4, with original tunnel structures have been synthesized. The first one crystallizes in the space group P21/n with image, image, image, image, and the second one in the space group Cc with image, image, image, image. β-Ba(MoO)2(P2O7)2 shows close relationships with the α-form, i.e., it consists of similar MoP2O11 units sharing their apices and forming [MoP2O10]∞ chains. It differs from the latter by the configuration of the chains, so that one chain is linked to four other identical chains, instead of six chains in the α-form. Like the α-form, the β-form exhibits intersecting tunnels running along [010] and [011] direction where the Ba2+ cations sit. The 3D-framework of the second phosphate Ba(MoO)2O(P2O7)PO4, is built up of MoO6 octahedra, P2O7 groups, and PO4 tetrahedra, can be described by the assemblage of zig-zag [Mo2P2O14]∞ chains through PO4 tetrahedra, forming large tunnels running along image, occupied by Ba2+ cations. In this framework one observes that adjacent tunnels communicate through large six-sided windows, showing the opened character of this structure. The magnetic behaviour of these phosphates is discussed with respect to the results previously obtained by Canadell et al. [Chem. Mater. 9 (1997) 68].