The Rare Earth Carbides R4C5 with R=Y, Gd, Tb, Dy, and Ho

Author： Czekalla R. Hufken T. Jeitschko W. Hoffmann R.D. Pottgen R.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.132, Iss.2, 1997-09, pp. : 294-299

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

The five carbides R4C5 (R=Y, Gd-Ho) have been prepared by arc-melting cold-pressed pellets of the elemental components and subsequent annealing at 1050°C. They crystallize with a new orthorhombic structure type (Pbam, Z=2), which has been determined from X-ray powder diffractometer data of Y4C5 (a=657.35(9) pm, b=1191.8(1) pm, c=366.92(5) pm, RF=0.035 for 179 structure factors) and also refined from powder data of Tb4C5 (a=660.8(1) pm, b=1197.3(2) pm, c=368.71(6) pm, RF=0.035 for 181 F values) and Ho4C5 (a=653.00(8) pm, b=1184.6(1) pm, c=363.80(4) pm, RF=0.036 for 171 F values and 10 positional parameters each). The structure contains building blocks, which were also found in the two closely related structures of alpha- and beta-Ho4C7. One-fifth of the carbon atoms are isolated from each other and coordinated octahedrally by rare earth atoms. The other carbon atoms form pairs with C-C bond distances of 133.5(15), 136(3), and 129(2) pm in Y4C5, Tb4C5, and Ho4C5, respectively, corresponding to C-C double bonds. Hence, all valence electrons can be accommodated in bonding R-C and C-C states according to the formula (R+3)4(C-42)2C-4, where the superscripts represent oxidation numbers. Nevertheless, the hydrolyses of Y4C5 and Ho4C5 with distilled water resulted in up to 41 wt% ethane, up to 16 wt% propane and propene, and up to 18 wt% higher hydrocarbons in addition to the expected products methane and ethylene.