Ca₁₁E₃C₈ (E = Sn, Pb): New Complex Carbide Zintl Phases Grown from Ca/Li Flux

Abstract

New carbide Zintl phases Ca(11)E(3)C(8) (E = Sn, Pb) were grown from reactions of carbon and heavy tetrelides in Ca/Li flux. They form with a new structure type in space group P2(1)/c (a = 13.1877(9)Å, b = 10.6915(7)Å, c = 14.2148(9)Å, β = 105.649(1)°, and R(1) = 0.019 for the Ca(11)Sn(3)C(8) analog). The structure features isolated E(4-) anions as well as acetylide (C(2)(2-)) and allenylide (C(3)(4-)) anions; the vibrational modes of the carbide anions are observed in the Raman spectrum. The charge-balanced nature of these phases is confirmed by DOS calculations which indicate that the tin analog has a small band gap (E(g) < 0.1 eV) and the lead analog has a pseudogap at the Fermi level. Reactions of these compounds with water produce acetylene and allene.

Ca12InC13–x and Ba12InC18H4: Alkaline-Earth Indium Allenylides Synthesized in AE/Li Flux (AE = Ca, Ba)

“…In the solids, these C 3 4– species are nearly linear, with C–C bond lengths that clearly indicate double bonds [1.304(4) Å and linear in the calcium compound; 1.325(7) Å with a 171° angle in the barium phase). Very similar bond lengths (in the 1.30–1.33 Å range) are seen in charge-balanced allenylide salts such as Mg 2 C 3 , Ca 3 C 3 Cl 2 , LiCa 2 C 3 H, and Ca 11 Sn 3 C 8 , as well as in metallic carbides including Ln 4 C 7 , Sc 3 C 4 , and R 5 Re 2 C 7 . ,,,,− The packing of the C 3 4– anions is different in Ca 12 InC 13– x and Ba 12 InC 18 H 4 , as shown in Figure . In both compounds, these linear anions are aligned parallel to the axes of the unit cell and positioned between the In@AE 12 icosahedral clusters.…”

“…This is comparable to the C 3 4− bending mode observed for Ca 11 Sn 3 C 8 (δ = 589 cm −1 ). 2 No corresponding peak is seen for Ca 12 InC 13−x ; the higher site symmetry of the C 3 4− anions in this structure may make this mode Raman inactive. The energies of the stretching modes of the allenylide anion are likely correlated to the electronegativity of the surrounding cations.…”

“…Depending on the reactant ratio, the p-block elements accept electrons and/or form M–M bonds to fill their valence shells . For instance, tin can exist in Zintl phases as isolated Sn 4– anions (in Ca 11 Sn 3 C 8 ), clusters such as Sn 4 4– (in Na 4 Sn 4 ) and Sn 9 4– (K 4 Sn 9 ), or anionic layers or networks as in K 8 Sn 44 . , However, a “Zintl border” exists between groups 13 and 14; group 13 metals are typically not electronegative enough to form Zintl anions. Elements such as gallium and indium therefore exhibit a rich and unpredictable chemistry.…”

Low-Dimensional Nitridosilicates Grown from Ca/Li Flux: Void Metal Ca8In2SiN4 and Semiconductor Ca3SiN3H

“…Recent work in our lab has focused on the use of Ca/Li flux. The successful growth of new carbide, hydride, and nitride phases such as Ca 12 InC 13‑ x , Ca 54 In 13 B 4‑ x H 23+ x , Ca 11 Sn 3 C 8 , and Ca 6 Te 3 N 2 from this melt indicates that further exploration is merited. − Calcium metal melts above 800 °C, but a 1:1 mixture of calcium with lithium metal melts at 300 °C. Such lowered temperatures enable incorporation of calcium into metastable nitride products; lithium more often acts as a spectator in the low temperature reaction, but will incorporate into products occasionally (as seen for Ca­(Li x Fe 1– x )­Te 2 N 3 , LiCa 3 As 2 H, and Ca 2 LiC 3 H). − …”

Metal Nitrides Grown from Ca/Li Flux: Ca6Te3N2 and New Nitridoferrate(I) Ca6(LixFe1–x)Te2N3

“…While electronegative main group elements are especially soluble in electropositive Ca/Li mixtures, light elements are also highly reactive in these melts. Previous reactions utilizing Ca/Li flux have produced compounds such as Ca 12 InC 13– x , Ca 54 In 13 B (4– x ) H (23+ x ) , Ca 11 E 3 C 8 (E = Sn, Pb), LiCa 3 As 2 H, LiCa 7 Ge 3 H 3 , and Ca 2 LiC 3 H. − Based on the successful syntheses of complex metal carbides and hydrides from refractive light element sources, it was postulated that Ca/Li flux may also be useful for the synthesis of complex nitrides.…”