EuPdIn2, YbPdIn2, and YbAuIn2: Syntheses, structures, and properties of new intermetallic compounds with ordered Re3B-type structure

The new compounds EuPdIn2 (1), YbPdIn2 (2), and YbAuIn2 (3) have been synth esized by high-frequency melting of the elements in sealed tantalum tubes a nd subsequent annealing at about 900 K. Their crystal structures have been determined by single-crystal X-ray diffraction techniques. Compounds 1, 2, and 3 crystallize with the MgCuAl2-type structure (space group Cmcm), a ter nary ordered version of the Re3B type, Structural elements in these compoun ds are transition metal centered trigonal prisms made up of the rare earth and indium atoms. The transition metal (T) and indium atoms form a three-di mensionally infinite [TIn2] polyanionic network in which the large rare ear th metal atoms occupy one-dimensional pentagonal tubes. A semiempirical ban d structure calculation on 1 reveals a non-vanishing density-of-states (DOS ) at the Fermi level. The strongest bonding interactions are found for the In-In and Pd-In contacts; the Eu-Pd and Eu-In interactions are much weaker. Magnetic investigations indicate divalent character of the ytterbium atoms in 2, showing negative susceptibilities below room temperature. Compound 1 exhibits Curie-Weiss behavior above 50 K with an experimental magnetic mom ent of 7.8(1) mu(B), thus indicating divalent europium. Ferromagnetic order ing was observed at T-C = 14.5(5) K, with a saturation moment of 6.8(1) mu( B)/Eu at 5.5 T and 4 K, as determined from magnetization measurements. Comp ounds 1 and 2 are found to be metallic conductors.