R. Czekalla et al., PREPARATION, CRYSTAL-STRUCTURE, AND PROPERTIES OF THE LANTHANOID CARBIDES LN(4)C(7) WITH LN=HO, ER, TM, AND LU, Zeitschrift fur Naturforschung. B, A journal of chemical sciences, 51(5), 1996, pp. 646-654
The isotypic carbides Ln(4)C(7) (Ln = Ho, Er, Tm, Lu) were prepared by
are-melting of the elemental components, followed by annealing at 130
0 degrees C. The positions of the metal and of some carbon atoms of th
e monoclinic crystal structure of Lu4C7 were determined from X-ray pow
der data, and the last carbon positions were found and refined from ne
utron powder diffraction data: P2(1)/c, a = 360.4(1), b = 1351.4(3), c
= 629.0(2) pm, beta = 104.97(2)degrees, Z = 2, R = 0.026 for 429 stru
cture factors and 15 positional parameters. The structure contains iso
lated 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 m
ay therefore be considered as derived from methane and propadiene. The
hydrolysis of Lu4C7 with distilled water yields mainly methane and pr
opine, while the hydrolyses of the corresponding holmium and erbium ca
rbides resulted in relatively large amounts of saturated and unsaturat
ed C-2-hydrocarbons in addition to the expected products methane and p
ropine. The structure comprises two-dimensionally infinite NaCl-type b
uilding elements, which are separated by the C-3-units, It may be desc
ribed as a stacking variant of a previously reported structure of Ho4C
7, now designated as the alpha-modification. The Lu4C7-type beta-modif
ication 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 par
amagnetic; beta-Ho4C7 and Er4C7 show Curie-Weiss behavior with magneti
c ordering temperatures of less than 20 K.