Square Pyramidal Clusters in La3In5 and Y3In5. La3In5 as a Metallic Zintl Phase

Abstract

The structures of the isostructural La3In5 and β-Y3In5, Pu3Pd5-type, have been refined and analyzed (Cmcm, Z = 4, a = 10.345(4) Å, 9.840(3) Å, b = 8.424(6) Å, 8.002(9) Å, c = 10.643(6) Å, 10.315(5) Å, R/Rw = 1.9/2.1, 2.4/2.4%, respectively). A somewhat slow first-order phase transition of the latter to (α)Y3In5 (Tm3Ga5-type) occurs in the neighborhood of 900–1000 °C (Pnma, Z=4,a= 12.219(7) Å,b= 10.328(7) Å, c = 6.424(3) Å, R/Rw, = 5.0/5.1%). The former structures contain well-defined indium square pyramids (C2v, d(In-In) ~ 3.0- 3.2 Å) with minimum intercluster separations of 3.43 and 3.58 Å in the larger lanthanum compound, 0.2–0.3 Å less in β-Y3In5. Clusters in the low-temperature (α)Y3In5 phase have been twisted and joined by short bonds at trans-basal positions into chains that are more weakly interconnected (as above) into a three-dimensional structure. All three phases are poorly metallic (ϱ295 ~ 90, 47, 47 μΩ cm, respectively) and Pauli-paramagnetic-like, La3In5 having the smallest χm value (4 × 10−4 emu mol−1). The apparent In59− cluster in La3In5 can in the classical limit be readily described as a closed shell, nido-deltahedron, and the compound structurally, as a Zintl phase. The obviously important bonding that gives such clear definition of clustering makes it appropriate to refer to La3In5 as a “metallic Zintl phase”, downplaying the derealization of a few of the least tightly bound electrons. © 1995, American Chemical Society. All rights reserved.