A Mixed-Valent Molybdenum Monophosphate with a "Butterfly"-Shaped Tunnel Structure Cs6Mo7O9(PO4)7 · H2O

Abstract

A new mixed-valent molybdenum monophosphate Cs6Mo7O9(PO4)7 · H2O has been isolated by solid state chemistry. It crystallizes in the space group Pnma with a = 10.084(1) Å, b = 21.297(3) Å, c = 17.491(1) Å. Its framework [Mo7P7O37]∞ consists of two kinds of structural units formulated Mo4P6O30 and Mo3PO16. The Mo4P6O30 units are built up from two edge-sharing MoO6 octahedra sharing their corners with two other MoO6 octahedra and six PO4 tetrahedra, whereas the Mo3PO16 units, which also exhibit two edge-sharing octahedra, can be derived from the first type of units by removing one octahedron and five tetrahedra. The structure can then be described by the association of [Mo4P6O28]∞ layers, built up of corner-sharing Mo4P6O30 units, with [Mo3PO15]∞ chains, built up of corner-sharing Mo3PO16 units. A comparison with leucophosphite is made. The host lattice [Mo7P7O37]∞ delimits two kinds of tunnels running along a: a large butterfly-shaped tunnel where the Cs+ ions and H2O molecules are located, and smaller tunnels occupied by Cs+ ions only. Besides these tunnels, cages are also obtained, fully occupied by Cs+ ions. The ordered distribution of Mo(V) and Mo(IV) species is also demonstrated: Mo(V) sits in MoO6 octahedra that exhibit one free apex, whereas Mo(IV) sits in the edge-sharing octahedra of the Mo4P6O30 units.