Preparation, Crystal Structure, and Properties of the Lanthanoid Carbides Ln₄C₇ with Ln = Ho, Er, Tm, and Lu

Abstract

The isotypic carbides Ln4C7 (Ln = Ho, Er, Tm, Lu) were prepared by arc-melting of the elemental components, followed by annealing at 1300 °C. The positions of the metal and of some carbon atoms of the monoclinic crystal structure of LU4C7 were determined from X-ray powder data, and the last carbon positions were found and refined from neutron powder diffraction data: P21/c, a = 360.4(1), b = 1351.4(3), c = 629.0(2) pm, β = 104.97(2)°, Z = 2, R = 0.026 for 429 structure factors and 15 positional parameters. The structure contains isolated carbon atoms with octahedral lutetium coordination and linear C3-units, with C-C bond lengths of 132(1) and 135(1) pm. This carbide may therefore be considered as derived from methane and propadiene. The hydrolysis of LU4C7 with distilled water yields mainly methane and propine, while the hydrolyses of the corresponding holmium and erbium carbides resulted in relatively large amounts of saturated and unsaturated C2-hydrocarbons in addition to the expected products methane and propine. The structure comprises two-dimensionally infinite NaCl-type building elements, which are separated by the C3-units. It may be described as a stacking variant of a previously reported structure of HO4C7, now designated as the a-modification. The Lu4C7-type β -modification was obtained at higher temperatures. Its structure was refined by the Rietveld method from X-ray powder data to a residual R = 0.037 for 320 F values and 15 positional parameters. Lu4C7 is Pauli paramagnetic; β -HO4C7 and Er4C7 show Curie-Weiss behavior with magnetic ordering temperatures of less than 20 K.

Ca2LiC3H: A New Complex Carbide Hydride Phase Grown in Metal Flux

“…Reaction of a compound containing the C 3 4− unit with a protic reagent should yield gaseous C 3 H 4 , as was reported for Mg 2 C 3 and R 4 C 7 . , Ca 2 LiC 3 H reacts rapidly and violently with water. A more controllable protolysis reaction was carried out using ammonium chloride as the source of acidic protons via its thermal decomposition to gaseous HCl and ammonia, following the procedure of a similar study on Mg 2 C 3 .…”

“…The title compound is one of a very small number of inorganic compounds containing the C 3 4− anion. This chain of three carbons, which can be viewed as deprotonated propadiene (C 3 H 4 , also known as allene), is also found in Mg 2 C 3 , Sc 3 C 4 , R 4 C 7 (R = Y, Ho, Er, Tm, Lu), R 5 Re 2 C 7 (R = Sc, Er, Tm, Lu), and Ca 3 C 3 Cl 2 . ,,− In Ca 2 LiC 3 H, this anion is perfectly linear, with the central carbon located on a center of inversion. The C−C bond length of 1.3254(9) Å is similar to that in propadiene (∼1.31 Å), indicating its double bond nature; the other reported structures containing the C 3 4− unit also feature a C−C bond of similar length (range: 1.32−1.35 Å).…”

The Rare Earth CarbidesR4C5withR=Y, Gd, Tb, Dy, and Ho

“…Hence, one could expect that about 78 wt% of the reaction products would be ethylene. However, this is not the case, as is usually observed for binary and ternary rare earth carbides (3,15,16). Only Al C and CaC yield the expected products methane and acetylene, respectively.…”

“…Only Al C and CaC yield the expected products methane and acetylene, respectively. Mg C produces mainly propyne instead of the expected propadiene (17,18), while the carbides of the rare earth elements usually produce a great variety of hydrocarbons including products with more than three carbon atoms (3,15,16). Lu C is an exception probably because the filled f shell may be important in the transition states of the reaction kinetics (3).…”

Ca12InC13–x and Ba12InC18H4: Alkaline-Earth Indium Allenylides Synthesized in AE/Li Flux (AE = Ca, Ba)

“…It is notable that no calcium methanide exists with comparable monatomic C 4– anions. While the methanide Be 2 C is the stable binary carbide for beryllium and a high-pressure magnesium methanide Mg 2 C was recently reported, no methanides are known for the heavier alkaline earths; those MC 2 metal carbides (M = Ca, Sr, Ba) contain acetylide anions instead. , Ca 12 InC 13– x is also one of a select few metal carbides featuring two different types of carbide anion; monatomic C 4– and the triatomic allenylide anion C 3 4– (vide infra) are also found in Ln 4 C 7 (Ln = Ho, Er, Tm, Lu), Sc 3 C 4 , and R 5 Re 2 C 7 (R = Er, Tm, Lu, Sc). − …”