Ce₁₀Cl₄Ga₅ and Ln₃ClGa₄ (Ln = La, Ce): Reduced Halides or Oxidized Intermetallics?

The compounds Ce10Cl4Ga5 and Ln3ClGa4 (Ln = La, Ce) were synthesized from stoichiometric mixtures of Ln, LnCl3, and Ga under Ar atmosphere in sealed Ta ampules at 910−1020 °C for 25−26 days. Ce10Cl4Ga5 is isostructural to La10Cl4Ga5 (space group I4/mcm, No. 140) with lattice constants a = 7.9546(11) Å, c = 31.793(6) Å. Ln3ClGa4 represents a new structural type, also in the space group I4/mcm, with a = 8.1955(8) and 8.1123(11) Å, c = 11.363(2) and 11.229(2) Å, respectively, for Ln = La and Ce. Ce10Cl4Ga5 features building blocks of Ga-centered Ce6 trigonal prisms and distinctive two-dimensional intermetallic CuAl2 and U3Si2 type nets. Its electronic structure falls within the realm of reduced rare-earth halides. Ln3ClGa4 also contains the intermetallic CuAl2 type nets, but the interstitials are inverted: The building blocks are Cl-centered Ln6 octahedra. Its electronic structure is characterized by strong peripheral Ln−Ga bonding stabilizing the Ln6Cl 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.