Configuration of the dimolybdate in salt inclusion type of compounds, Cs2Mo2O7 ⋅ CsX (X=Cl, Br, and I)

Abstract

Cs2Mo2O7 ⋅ CsI is obtained as a member of the series Cs2Mo2O7 ⋅ CsX with X=Cl, Br, and I from the synthesis of Cs2MoO4 with MoO3 and CsX. At room temperature, the compounds crystallize in the space group P63/mmc with the dimolybdate, [Mo2O7]2−, in a linear and eclipsed conformation. Low temperature Raman spectroscopy and low temperature X-ray diffraction were used to investigate the effect of the urn:x-wiley:00442313:media:zaac202300199:zaac202300199-math-0001 hetero-honeycomb lattice on the bridging angle of the dimolybdate. For X=Cl, a phase transition occurs below 150 K (P63/mmc → Cmcm). The phase transition relates to a lock-in that involves bending of the (Mo−O−Mo) bridge. For the Pearson softer iodide compound, no phase transition is observed down to 4 K; thus, the linear configuration remains stable. Specific heat data and their evaluation in terms of phonon contributions are given.