THE HIGH-TEMPERATURE (BETA) MODIFICATION OF Y4C7 WITH LU4C7 TYPE AND DY3C4 WITH SC3C4 TYPE-STRUCTURE

A new modification of Y4C7 has been prepared by are-melting of the ele mental components and subsequent annealing at 1300 degrees C. Its crys tal structure was refined from X-ray powder diffractometer data: P2(1) /c, a=372.6(1) pm, b=1369.2(2) pm, c=652.7(1) pm, P=103.03(1)degrees, Z=2, R=0.027 for 341 structure factors and 15 positional parameters. T he C-C distances in the propadienyl anion are 125(3) and 132(3) pm in good agreement with the average C-C distance of 132 pm found in the st ructures of the carbides beta-Ho4C7 and Lu4C7. The new carbide Dy3C4 h as a tetragonal Sc3C4 type structure with the lattice constants a=808. 3(1) pm and c=1588.1(3) pm. (C) 1998 Elsevier Science S.A. All rights reserved.