SYNTHESIS AND CRYSTAL-STRUCTURES OF THE T ERNARY RARE-EARTH CHLORIDESNAMCL(4) (M=EU-YB, Y)

Single crystals of NaErCl4 were obtained from the melt of NaCl. and Er Cl3 (1:1 molar ratio) by slow cooling. It crystallizes in the monoclin ic crystal system (space group P2/c) with the structure of alpha-NiWO4 with a = 632.24(9) pm, b = 759.78(9) pm, c = 674.2(1) pm, P = 92.310( 3)degrees, Z = 2. Two preparative routes to pure powder samples of the chlorides NaMCl(4) are described. At room temperature, these are foun d to be isotypic with NaErCl4 (M = Tm-Yb; II) while the triclinic stru cture of NaGdCl4 is adopted with M = Gd-Ho, Y (I). Phase transitions f rom one structure to the other are observed for all compounds. The tra nsition temperatures decrease with decreasing size of the ion M(3+).