Phase formation features in the systems M2MoO 4–Fe 2(MoO 4) 3 ( M=Rb, Cs) and crystal structures of new double polymolybdates M3FeMo 4O 15

Abstract

The systems M 2MoO 4–Fe 2(MoO 4) 3 ( M=Rb, Cs) were shown to be non-quasibinary joins of the systems M 2O–Fe 2O 3–MoO 3. New compounds M 3FeMo 4O 15 were revealed along with the known MFe(MoO 4) 2 and M 5Fe(MoO 4) 4. The unit cell parameters of the new compounds are a=11.6192(2), b=13.6801(3), c=9.7773(2) Å, β=92.964(1)°, space group P2 1/ c, Z=4 ( M=Rb) and a=11.5500(9), b=9.9929(7), c=14.513(1) Å, β=90.676(2)°, space group P2 1 /n, Z=4 ( M=Cs). In the structures of M 3FeMo 4O 15 ( M=Rb, Cs), a half of the FeO 6 octahedra share two opposite edges with two MoO 6 octahedra linked to other FeO 6 octahedra through the bridged MoO 4 tetrahedra by means of the common oxygen vertices to form the chains along the a axis. The difference between the structures is caused by diverse mutual arrangements of the adjacent polyhedral chains.