GaMgMo4O7 and Fe2Mo4O7 -: two low-valent molybdenum oxides with a fully ordered Sc0.75Zn1.25Mo4O7 type structure

The title compounds have been prepared by sintering at 1200 degreesC. Their crystal structures have been determined from single crystal diffractometer data: space group Imma, with a=6.016(3), b-5.712(1), c 16.606(4) Angstrom (GaMgMo4O7) and a=6.018(1), b=5.782(1), c=16.901(5) Angstrom (Fe2Mo4O7), Z=4. The structure is interpreted as 3 substitutional derivative nf a cubic closed-packing of oxygen ions with the molybdenum cluster atoms occupying octahedral holes. While gallium is in tetrahedral and magnesium in octahedral oxygen coordination, bond valences suggest that iron(II) is in the tetrahedral and iron(III) in the octahedral sites. (C) 2001 Elsevier Science B.V. Ail rights reserved.