Dicaesium tetra-magnesium penta-kis-(carbonate) deca-hydrate, Cs 2 Mg 4 (CO 3 ) 5 ·10H 2 O.

The title carbonate hydrate, CsMg(CO)·10HO, was crystallized at room temperature out of aqueous solutions containing caesium bicarbonate and magnesium nitrate. Its monoclinic crystal structure (2/) consists of double chains of composition [Mg(HO)(CO)], isolated [Mg(HO)(CO)] units, two crystallographically distinct Cs ions and a free water mol-ecule. The crystal under investigation was twinned by reticular pseudomerohedry.