Ca11E3C8 (E = Sn, Pb): new complex carbide Zintl phases grown from Ca/Li flux.

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.