Synthesis,Chraracrerization,and Structural and Theoretical Analysis of Gd_4B_3C_4:A Novel Rare Earth metal Borocarbide Containing Two Different Boron-Carbon Arrangements

摘要

The synthesis by arc-melting techniques, the single-crystal_X-ray structure, and the theoretical analysis of GcLB~C. are reported. It crystallizes in the triclinic space group P1 with a = 3.637(2) A, b = 3.674(2) A, c = 11 .8~ ~, A, a. = 93·34(5)0, ~3 = 96.77(5)0, y = 90.24(5)0, and Z = 1. In this structure, the boron and carbon atoms form two different types of nonmetal arrangements: l-D (BCX.~ branched chains and finite (0-D) linear CBC “moleculaiK’ units. Gd4B3C4 is the first characterized member of the rare earth metal borocarbide series in which both 1 -D and “molecular” 0-D nonmetal atom systems coexist. From the structural and theoretical analysis, the following formal charge distribution can be proposed within the ionic limit: (Gd3~)4(BCj)(BC3)2.e. Tight-binding calculations suggest that the excess electron in the ionic limit is mainly localized on the Gd atoms (at the bottom of the Sd band). while LAPW calculations favor its localization on the (BCX. chain. The bonding within this compound is fully analyzed and compared to other members