Structural relationships between new carbide La14Sn(MnC6)3 and fully ordered La11(MnC6)3

Crystals of the ternary La11(MnC6)3 and new quaternary carbide La14Sn(MnC6)3 phases were grown from La/Ni eutectic flux and their structures were determined by means of X-ray single crystal diffraction. La11(MnC6)3 is a new superstructure variant of La3.67MnC6 (previously reported disordered subcell: P63/m; a0=8.806 Å; c0=5.329 Å, Z=2). The superstructure (R3¯; a=√3a0=15.2649(9) Å; c=3c0=16.013(1) Å, Z=6; R1=0.022) is realized by complete ordering of the La chains within the columns of face-sharing carbon octahedra, with alternating La–La distances leading to R-centering and enlargement of the unit cell. The structure of the quaternary carbide La14Sn(MnC6)3 (P6¯; a=8.756(1) Å; c=10.483(2) Å, Z=1; R1=0.026) is closely related to that of La11(MnC6)3 with part of the MnC6 units replaced by Sn atoms. The structure and precise composition of La14Sn(MnC6)3 can be derived from that of La11(MnC6)3 by taking into account the extent of this substitution and variation in lanthanum siting in the chain of carbon octahedra. Band structure calculations indicate both phases are metallic; the La11(MnC6)3 phase is stabilized by the ordering of La atoms which induces a pseudogap at EF.

La11(MnC6)3 with fully ordered superstructure and a new carbide La14Sn(MnC6)3 were obtained from La/Ni eutectic flux.Figure optionsDownload as PowerPoint slide