La_3Ir_2 with Rhombohedral Er_3Ni_2- type Structure

摘要

La_3Ir_2 is formed upon reaction of the elements at 1273 K in a sealed silica ampoule. The structure was refined from single-crystal X-ray diffractometer data: Er_3Ni_2-type structure, R3-bar, a=895.26(2), c=1713:01(5) pm, wR=0.0578, 766 F2 values, 25 variables. The structure is composed of two simple basic building units: slightly distorted La1@La3_6La2_2 cubes resembling the tungsten structure and Ir_2@La1_1La2_2La3_5 units with an AlB2-related coordination (298 pm Ir-Ir in the dumb-bell). Each cube is coordinated by six of the AlB_2 units. The relationship with the U_3Si_2-type structure is discussed.