A Mixed-Valence Molybdenum Monophosphate with a Three-Dimensional Framework: LiMo 2 O 3 (PO 4 ) 2

Author： Ledain S. Leclaire A. Borel M.M. Raveau B.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.124, Iss.2, 1996-07, pp. : 322-328

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Abstract

A new mixed-valence monophosphate possessing a unique structure type, LiMo 2 O 3 (PO 4 ) 2 , has been synthesized. It crystallizes in the P 2 1 / m space group with a = 7.771 (1) A, b = 12.687 (2) A, c = 8.445 (2) A, beta = 106.94 (1)#°. Its three-dimensional [Mo 2 P 2 O 11 ] [infinity] framework consists of two kinds of [Mo 2 P 2 O 15 ] [infinity] chains. The first kind of chain running along [101] is built up from "Mo 2 PO 13 " units linked through single PO 4 tetrahedra; the second kind of chain, running along [100] is similar to that encountered in W 2 O 3 (PO 4 ) 2 . This framework is also described by the three-dimensional assemblage of [MoPO 8 ] [infinity] chains, running along b. One recognizes two sorts of small tunnels running along b and a, respectively. The second kind of tunnel exhibits a similarity with that observed in the brownmillerite structure. Another novelty of this structure deals with the existence of two coordinations for lithium: tetrahedral and octahedral. The octahedral lithium ions obstruct the tunnels running along a and share two oxygen atoms with Mo(1) corresponding to the free vertices of the MoO 6 octahedra; the tetrahedral lithium ions share one oxygen atom with Mo(2), and one oxygen with Mo(3) corresponding to the free vertex of the Mo(3)O 6 octahedron.