Ternary rare earth metal boride carbides containing two-dimensional boron–carbon network: The crystal and electronic structure of R2B4C (R=Tb, Dy, Ho, Er)

The ternary rare earth boride carbides R₂B₄C (R=Tb, Dy, Ho, Er) have been synthesized by reacting the elements at temperatures between 1800 and 2000K. The crystal structure of Dy₂B₄C has been determined from single-crystal X-ray diffraction data. It crystallizes in a new structure type in the orthorhombic space group Immm (a=3.2772(6) Å, b=6.567(2) Å, c=7.542(1) Å, Z=2, R1=0.035 (wR₂=0.10) for 224 reflections with I_o>2σ(I_o)). Boron atoms form infinite chains of fused B₆ rings in 100] joined with carbon atoms into planar, two-dimensional networks which alternate with planar sheets of rare earth metal atoms. The electronic structure of Dy₂B₄C was also analyzed using the tight-binding extended Hückel method.