SYNTHESIS, CRYSTAL-STRUCTURE, MAGNETISM, AND ABSORPTION-SPECTRA OF A2UX5 TYPE HALIDES (A=K, RB, X=CL, BR, I)

The ternary uranium(III) halides A2UX5 (A = K, Rb; X = Cl, Br, I) have been prepared from the binary components AX and UX3 in sealed tantalu m containers. According to their Guinier X-ray powder patterns, they a ll crystallize with the K2PrCl5/Y2HfS5 type of structure. Lattice cons tants for ambient temperature are reported. Single-crystal structure r efinemens were undertaken for K2UI5 and Rb2UCl5. Magnetic susceptibili ty data were recorded with a SQUID magnetometer from liquid helium to room temperature. One-dimensional (intrachain) and three-dimensional a ntiferromagnetic ordering occur at low temperatures dependent upon the U3+-U3+ distance. Absorption spectra were recorded between 4000 and 2 8000 cm-1. They show f-f transitions typical for U3+ and, depending on the halide, very strong f-d transitions above 14000 to 15000 cm-1, re spectively.