Synthesis, Structure, and Bonding of Two Lanthanum Indium Germanides with Novel Structures and Properties.
The new tetragonal phases La(3)In(4)Ge and La(3)InGe are obtained from high-temperature reactions of the elements in welded Ta followed by annealing. The structures of both were established by single-crystal X-ray diffraction in tetragonal space group I4/mcm (Z = 4 and 16, a = 8.5165(3) and 12.3083(2) Å, c = 11.9024(4) and 16.0776(4) Å, respectively). La(3)In(4)Ge contains layers or slabs of three-connected indium built of puckered 8-rings and 4-rings, or of squashed tetrahedra ("butterflies") interlinked at all vertices, and these are separated by layers of La and isolated Ge. The phase is deficient of being a Zintl phase by three electrons per formula unit and is better described in terms of an alternate optimized and delocalized bonding picture and an open-shell metallic behavior for the In slabs. The more complex La(3)InGe, isostructural with Gd(3)Ga(2), is also layered. This phase contains pairs of mixed-occupancy (0.75 In, 0.25 Ge) sites separated by 3.020 Å, as well as isolated In and Ge atoms. The former appear to be fully reduced closed-shell atoms (relative to the bonded Ga dimers in Gd(3)Ga(2)) that are held in somewhat close proximity by cation matrix effects. The compound appears to be semiconducting and thus is a classical Zintl phase, (La(+3))(3)In(-5)Ge(-4) in the simplest oxidation state notation. High Coulomb energies are presumably important for the nature of the bonding and the stabilities of both compounds.
Guloy
Arnold M.
AM
Department of Chemistry and Ames Laboratory-DOE,(1) Iowa State University, Ames, Iowa 50011.
Corbett
John D.
JD