Ternary Rare Earth Metal Silicides RE2RE’3Si4 with Orthorhombic Sm5Ge4 or Tetragonal Zr5Si4 Type Structure

Abstract

Ternary silicides RE2RE′3 Si4 (RE = La, Ce; RE′= Y, Lu) were synthesized by arc-melting of the elements. Single crystals were grown by annealing the arc-molten buttons slightly below the melting points in water-cooled silica tubes in an induction furnace. Five silicides RE2RE3′Si4 were investigated by X-ray powder and single crystal diffraction: Zr5Si4 type, P41212, a = 779.4(3), c = 1441.3(9) pm, wR2 = 0.072, 1806 F2 values, 45 variables for La1.72(4)Y3.28(4)Si4, P43212, a = 769.92(7), c = 1412.3(1) pm, wR2 = 0.079, 1846 F2 values, 45 variables, BASF = 0.36(4) for La1.72(2)Lu3.28(2)Si4, P41212, a = 778.6(1), c = 1433.9(3) pm, wR2 = 0.054, 1910 F2 values, 46 variables, BASF = 0.34(4) for Ce1.82(6)Lu3.18(6)Si4, P43212, a = 778.8(3), c = 1436.0(10) pm, wR2 = 0.166, 1916 F2 values, 45 variables for Ce1.71(7)Y3.29(7)Si4, and Sm5Ge4 type, Pnma, a = 749.2(2), b = 1484.2(7), c = 780.3(2) pm, wR2 = 0.070, 1956 F2 values and 49 variables for Ce1.47(3)Y3.53(3)Si4. The local coordinations of both structure types are very similar, i. e. CN 18, 16, and 14 coordination polyhedra for the RE1, RE2, and RE3 atoms. The main structural motif is the eightfold coordination of the RE3 positions by rare earth metal atoms. These slightly distorted RERE’8 cubes are condensed via common corners (Zr5Si4 type) or via common edges (Sm5Ge4 type). All silicon atoms in these silicides form Si2 pairs at Si-Si distances ranging from 254 to 258 pm. DFT band structure calculations confirm the metallic character of both silicides and the trivalent state of cerium in Ce5Si4. The COHP analysis (Crystal Orbital Hamilton Population) of the Si-Si bonds shows a significant occupation of Si-Si antibonding orbitals, which is partially compensated by a Si-Si π*,σ*Y-4d (Ce-5d) back donation.