A mixed valent molybdenotungsten monophosphate with an original intersecting tunnel structure: Li(Mo,W)(2)O-3(PO4)(2)

A new molybdenotungsten monophosphate Li(Mo,W)(2)O-3(PO4)(2) with an intersecting tunnel structure has been synthesized. It crystallizes in the C2/m space group with a = 8.142(1) Angstrom, b = 6.361(1) Angstrom, c = 7.728(1) Angstrom, beta = 102.45(1)degrees. Its tridimensional framework consists of corner-sharing bioctahedral ''M(2)O(11)'' units and monophosphate PO4 groups forming [M(2)P(2)O(15)](infinity) chains running along c and [MPO(8)](infinity) chains running along b. The [M(2)P(2)O(11)](infinity) framework delimits six-sided intersecting tunnels running along [110], [(1) over bar 10], and [001], respectively. The lithium ions that are located at the intersection of these three kinds of tunnels, in the brownmillerite windows, exhibit an antiprismatic sixfold coordination. Close relationships with the two monophosphates MoxW2-xO3(PO4)(2) and LiMo2O3(PO4)(2) are evidenced. (C) 1997 Academic Press.