The Crystal Structures of the Hydrated Alkalimetal-/Rare Earth(III) Chlorides ALnCl4· 4H2O (A= NH4, K, Rb, Cs; Ln = La–Sm) and CsLaCl4· 3H2O

The crystal structures of the compounds RbLaCl4· 4H2O and CsNdCl4· 4H2O have been determined by single crystal X-ray analysis. These compounds precipitate from aqueous solution upon evaporation at 50°C. RbLaCl4· 4H2O (a= 1140.1 pm,b= 701.8 pm,c= 668.8 pm) and CsNdCl4· 4H2O (a= 1127.1 pm,b= 711.5 pm,c= 678.7 pm) crystallize in the orthorhombic space groupP21212 withZ= 2. The unit cell parameters of the isotypic compounds KLnCl4· 4H2O (Ln= Ce–Nd), NH4LnCl4· 4H2O (Ln = La–Pr), RbLnCl4· 4H2O (Ln= Ce–Sm), and CsLnCl4· 4H2O (Ln= Ce, Pr) were determined from powder patterns. The structure is composed of layers of edge-bridged polyhedra around both cations. The anionic part of the structure around the rare earth ions consists of the monomeric units [LnCl4(H2O)4]−. The coordination number of both the alkali- and the rare earth-ions is 8, independent of the changes in their ionic radii. Instead of the expected tetrahydrate “CsLaCl4· 4H2O” a trihydrate CsLaCl4· 3H2O was precipitated under the same conditions. This compound crystallizes with the CsUCl4· 3H2O-type structure with the coordination number 9 for La.