Crystal structures of caesium and rubidium chlorochromates,CsCrO3Cl and RbCrO3Cl

The crystal structures of CsCrO₃Cl and RbCrO₃Cl have been determined from MoK₁diffractometer data and refined anisotropically toR = 0.029 andR = 0.033 respectively for 769 and 590 statistically significant reflections. CsCrO₃Cl, which has a structure of the BaSO₄ type, crystallizes in the orthorhombic space groupPnma, witha = 9.928,b = 6.043,c = 8.712 Å andZ = 4. RbCrO₃Cl is isostructural with KCrO₃C1 and NH₄CrO₃Cl and crystallizes in the monoclinic space groupP2₁/c witha = 7.857,b = 7.711,c = 8.055 Å, = 90.43 ° andZ = 4. The geometry of the approximately tetrahedral CrO₃Cl^– groups is very similar in both structures, and the Cr-Cl and average Cr-O bond distances, corrected for thermal vibration of the terminal atoms, are 2.197 and 1.612 Å in CsCrO₃Cl and 2.194 and 1.606 Å in RbCrO₃Cl. Caesium ions are in 12-fold coordination and rubidium ions in irregular 11-fold coordination to chlorine and oxygen.