1996/05/01 by Ralf Czekalla, Wolfgang Jeitschko, Rolf‐Dieter Hoffmann +1 · 2 citations
Engineering · Materials Science · #Advanced materials and composites #Metal and Thin Film Mechanics #Diamond and Carbon-based Materials Research
paper · pdf · doi:10.1515/znb-1996-0505
openalex publication_date 1996/05/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The isotypic carbides Ln 4 C 7 (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 LU 4 C 7 were determined from X-ray powder data, and the last carbon positions were found and refined from neutron powder diffraction data: P2 1 /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 C 3 -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 LU 4 C 7 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 C 2 -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 C 3 -units. It may be described as a stacking variant of a previously reported structure of H O4 C 7 , now designated as the a-modification. The Lu 4 C 7 -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. Lu 4 C 7 is Pauli paramagnetic; β -H O4 C 7 and Er 4 C 7 show Curie-Weiss behavior with magnetic ordering temperatures of less than 20 K.