Carbon pairs as structural elements of ternary carbides of the F elements with the late transition metals

Article abstract of DOI:10.1016/0022-5088(89)90434-7

The crystal structures of the carbides NdCoC₂ (CeCoC₂ type) and La₂Ni₅C₃ (own type) were refined from single-crystal X-ray data to residuals of R = 0.033 (358 structure factors, 26 variable parameters) and R = 0.019 (265 F values, 22 variables). The C-C distances of the C₂ pairs are 140(2) pm and 135.9(8) pm respectively. The near-neighbor concentrations of these C₂ pairs are discussed, together with those of related structures. The results of the hydrolyses with diluted hydrochloric acid of several ternary carbides are reported. The products range from methane, ethane and ethylene up to various isomers of hexane. There is little correlation between the C-C bonding (C₂ pairs with various bond lengths or isolated carbon atoms) and the amounts of the various hydrocarbons developed. La₂Ni₅C₃ does not become superconducting down to 1.8 K. Comparative extended Huckel calculations for various real and hypothetical transition metal carbide polyanions were carried out as a function of the number of valence electrons of the polyanions.