Synthesis and Crystal Structure of the Novel Compound Mg4.5Pr79.5Mo126O312 Containing Mo3, Mo7 and Mo19 Clusters

The synthesis and crystal structure of the novel reduced molybdenum oxide Mg4.5Pr79.5Mo126O312 are presented. This compound crystallizes in the trigonal space group R-3 m with a = 11.3061(2) Å, c = 58.242(1) Å, V = 6447.5(2) Å3, and Z = 1. Refinements yield R(F2) = 0.0433 and wR(F2) = 0.0931 for 2827 unique reflections. The structure is built up from alternating slabs made up of molybdenum forming Mo3, Mo7 and Mo19 clusters, praseodymium and oxygen atoms, and slabs containing isolated MoO6 octahedra. The Pr3+ cations are localized either within the slabs or at their borderlines to ensure the cohesion between the slabs. Of the six crystallographically independent sites occupy by the Pr3+ cations, two of them also contain randomly about 15% and 20% of Mg2+ cations while the remaining four are fully occupied by the Pr3+ cations.