Ce10Cl4Ga5 and Ln3CIGa4 (Ln = La, Ce): Reduced Halides or Oxidized Intermetallics?

The compounds Ce10Cl4Ga5 and .... (Ln = La, Ce) were synthesized from stoichiometric mixtures of Ln, LnCIs, and Ga under Ar atmosphere in sealed Ta ampules at 910-1020 °C for 25-26 days. ..... is isostructural to LaioCGas (space group 14/mcm, No. 140) with lattice constants a = 7.9546(11) A, c = 31.793(6) A. LnsCIGa4 represents a new structural type, also in the space group 14/mcm, with a == 8.1955(8) and 8.1123(11) A, c = 11.363(2) and 11.229(2) A, respectively, for Ln == La and Ce. CeicCGas features building blocks of Ga-centered Cee trigonal prisms and distinctive two-dimensional intermetallic CuA and UsS type nets. Its electronic structure falls within the realm of reduced rare-earth halides. LnsCIGa4 also contains the intermetallic CuA type nets, but the interstitials are inverted: The building blocks are Cl-centered Lne octahedra. Its electronic structure is characterized by strong peripheral Ln-Ga bonding stabilizing the LneCI octahedron which normally would have its Ln-Ln antibonding orbitals filled with electrons from interstitials beyond chalcogen. Magnetic susceptibility and conductivity measurements confirm the metallic nature of all three compounds.