Matrix effect in chevrel phases containing divalent metal cations. The structure of rhombohedral CaMo 6S 8

Abstract

The structure of CaMo 6S 8 was refined from single crystal X-ray data at 298 K (space group R 3, a = 6.5146(5) Å, α = 89.63(1)°, R = 0.032 for 720 reflections with I > 3 σ( I) and 25 parameters). Comparison with isoelectronic MMo 6S 8 ( M = Yb 2+, Eu 2+, Sr 2+, Ba 2+) confirms the matrix effect predicted by J. D. Corbett ( J. Solid State Chem. 39, 56 (1981)). As the cell volume increases across this series the Mo 6 cluster contracts along its ternary axes by 0.021(1) Å. The strengthening of the MoMo intracluster bonds correlates with a weakening of the MoMo and MoS intercluster bonds.