The crystal structures of the Chevrel phases Li(3.3)Mo(6)S (8) and Li(3.2)Mo(6)Se(8).

We have determined the crystal structures of Li(3.3)Mo(6)S (8) and Li(3.2)M0(6)Se(8), Chevrel phases formed by the insertion of lithium into Mo(6)S(8) and Mo(6)Se(8), by Neutron diffraction power profile analysis. The Mo(6)S(8) and Mo(6)Se(8) clusters are quite similar to those in other compounds of this type. The lithium atoms in both cases are disordered over the two concentric rings of available tetrahedrally coordinated small atom sites. For both compounds, occupancy of the outer ring is strongly preferred, and in Li(3.3)Mo(6)Se(8) the inner lithium ring has a unique puckered geometry.