The Metallic Zintl Phase Ba₃Si₄ – Synthesis, Crystal Structure, Chemical Bonding, and Physical Properties

Abstract

The Zintl phase Ba 3 Si 4 has been synthesized from the elements at 1273 K as a single phase. No homogeneity range has been found. The compound decomposes peritectically at 1307(5) K to BaSi 2 and melt. The butterfly-shaped Si 4 6Ϫ Zintl anion in the crystal structure of Ba 3 Si 4 (Pearson symbol tP28, space group P4 2 /mnm, a ϭ 8.5233(3) Å , c ϭ 11.8322(6) Å ) shows only slightly different Si-Si bond lengths of d(SiϪSi) ϭ 2.4183(6) Å (1ϫ) and 2.4254(3) Å (4ϫ). The compound is diamagnetic with χ ഠ Ϫ50 ϫ 10 Ϫ6 cm 3 mol Ϫ1 . DC resistivity measurements show a high electrical resistivity (ρ(300 K) ഠ 1.2 ϫ 10 Ϫ3 Ω m) with positive temperature gradient dρ/dT. The temperature dependence of the isotropic signal shift and the spin-lattice relaxation times in 29 Si 1651 NMR spectroscopy confirms the metallic behavior. The experimental results are in accordance with the calculated electronic band structure, which indicates a metal with a low density of states at the Fermi level. The electron localization function (ELF) is used for analysis of chemical bonding. The reaction of solid Ba 3 Si 4 with gaseous HCl leads to the oxidation of the Si 4 6Ϫ Zintl anion and yields nanoporous silicon.

Refinement of the crystal structure of dibarium tetrasilicide, Ba2Si4

“…The lattice parameters of Ba 2Si4 of these samples and those reported in [1] are equal within 3s of the standard deviation.…”

Toward a comprehensive definition of oxidation state (IUPAC Technical Report)

“…Some sp elements may also form stoichiometric metallic compounds. Ba 3 Si 4 obeys the Zintl concept [58] in that it forms butterfly-shaped Si 4 6-anions, in which two Si have two bonds and two Si have three bonds to each other according to the generalized 8−N rule (Section 7.4.1), yet the compound is weakly metallic [191].…”

The Zintl Phase Cs7NaSi8 – From NMR Signal Line Shape Analysis and Quantum Mechanical Calculations to Chemical Bonding

“…The results from FPLO and Wien2k for the calculated DOS were qualitatively identical showing the same contributions as already reported in Rb 7 NaSi 8 . [21] Comparison of QM calculated with experimentally determined NMR coupling parameters from previous studies on intermetallic phases -MGa 2 (M = Ca, Sr, and Ba) , [13] MGa 4 (M = Na, Ca, Sr, and Ba), [14] M 4 Si 4 (M = Na, Rb, K, and Cs) [20] as well as Ba 2 Si 4 [12] and Rb 7 NaSi 8 [21] and NaRb 7 (Si 4-x Ge x ) 2 [22] -indicates that a good agreement can be achieved within the following ranges: Ϯ 10 ppm for the NMR signal shift and shift anisotropy, Ϯ 0.1 MHz for C Q and Ϯ0.1 ϫ 10 21 V m -2 for V ZZ , respectively. In case of asymmetry parameters η ϶ 0, an error of Ϯ 0.05 can be estimated.…”