ABSTRACT
Reactions of anthracene in Ln/T eutectic mixtures (Ln = La, Yb; T = Ni, Cu) have produced crystals of new complex lanthanide carbide hydride phases. The thermal decomposition of anthracene provides a source of both carbon and hydrogen. LaCHx forms in space group Pnma with unit cell parameters a = 7.2736(4) Å, b = 3.7218(2) Å, and c = 13.0727(7) Å. Yb2CHx forms in space group P-3m1 with unit cell parameters a = 3.5659(4) Å and c = 5.8000(8) Å, with a structure related to that of Ho2CF2. The presence of hydride in interstitial sites is supported by the formation of different compounds in the absence of hydrogen and by comparison to known hydride structures. 1H nuclear magnetic resonance (NMR) spectra collected on LaCHx show two unique hydride resonances, in agreement with the two available interstitial sites. Density of states calculations show that filling the tetrahedral sites in LaCHx with hydrogen increases metallic behavior, while adding hydrogen into the tetrahedral sites in Yb2CHx induces the formation of a band gap.
ABSTRACT
La15(FeC6)4F2 was grown as large crystals by reacting iron in a La/Ni eutectic flux in the presence of decafluorobiphenyl (C12F10) which acts as both a carbon and fluoride source. This mild fluorinating technique enables the isolation of an intermetallic product containing fluoride interstitials, as opposed to forming ionic metal fluorides. The compound adopts a structure in the hexagonal crystal system with space group P6Ì which features FeC6 units composed of a central iron atom coordinated by three ethylenide units in a trigonal planar configuration. The structure is related to the previously reported La15(FeC6)4H, but with fluoride fully occupying the interstitial hydride positions, which induces partial occupancies and site splitting disorder in the adjacent layers of lanthanide ions. No supercell formation is observed.
