A large series of isotypic Mo(V) diphosphates with a tunnel structure: From A(MoO)10(P2O7)8 with A=Ba, Sr, Ca, Cd, Pb to A(MoO)5(P2O7)4 with A=Ag, Li, Na, K

The single crystal structure of a series of nine isotypic Mo(V) diphosphates was determined from crystals with composition A 2+(MoO)10(P2O7)8 (A=Ba, Sr, Ca, Cd, Pb) and A +(MoO)5(P2O7)4 (A=Ag, Li, Na, K). The structure of those phosphates, built up of corner sharing MoO6 octahedra, MoO5 tetragonal pyramids and P2O7 diphosphates groups, forms eight-sided tunnels as described by Lii et al. for A=Ag. New features are evidenced: (1) existence of two orientations, up and down along b for the MoO5 pyramids; (2) maximum insertion rate of the divalent cations which is twice less than that of the univalent cations; (3) different behavior of the series 'Pb, Sr, Ba, Li, Na, K' which exhibits only one kind of site for the inserted cation, compared to the 'Cd, Ca, Ag' series for which two kinds of sites are observed; (4) off-centering of the A-site cations with respect to the tunnel axis; and (5) unusually high thermal factors along the tunnel axis, but absence of ionic conductivity. - Graphical abstract: The structure of Pb(MoO)10(P2O7)8 viewed along b with the Pb ions in the octagonal tunnels