THE CRYSTAL-STRUCTURES OF THE HYDRATED ALKALIMETAL RARE EARTH(III) CHLORIDES ALNCL(4)CENTER-DOT-4H(2)O (A=NH4, K, RB, CS LN=LA-SM) AND CSLACL4-CENTER-DOT-3H(2)O

The crystal structures of the compounds RbLaCl4 . 4H(2)O and CsNdCl4 . 4H(2)O have been determined by single crystal X-ray analysis. These c ompounds precipitate from aqueous solution upon evaporation at 50 degr ees C. RbLaC4 . 4H(2)O (a = 1140.1 pm, b = 701.8 pm, c = 668.8 pm) and CsNdCl4 . 4H(2)O (a = 1127.1 pm, b = 711.5 pm, c = 678.7 pm) crystall ize in the orthorhombic space group P 2(1) 2(1) 2 with Z = 2. The unit cell parameters of the isotopic compounds KLnCl(4) . 4H(2)O (Ln = Ce- Nd), NH(4)LnCl(4) . 4H(2)O (Ln = La-Pr), RbLnC(4) . 4H(2)O (Ln = Ce-Sm ), and CsLnCl(4) . 4H(2)O (Ln = Ce, Pr) were determined from powder pa tterns. 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 [LnCl(4)(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 expect ed tetrahydrate ''CsLaCl4 . 4H(2)O'' a trihydrate CsLaCl4 . 3H(2)O was precipitated under the same conditions. This compound crystallizes wi th the CsUCl4 . 3H(2)O-type structure with the coordination number 9 f or La. (C) 1996 Academic Press, Inc.