Synthesis, Structure, and Vibrational Spectra of Al_3BC_3, a Carbidecarboborate of Aluminum with Linear (C=B=C)~(5-) Anions

摘要

Compounds of the Al/B/C system are of great importance for the development of light, nonoxidic ceramics because of their high chemical and thermal stability, which has led to a great number of recent publications and patents in this field. While boron-rich compounds such as B_(51)Al_2C_8 ("AlB_(10)",) and B_(48_Al_3C_2 ("diamond-like boron", "β-AlB_(12)") have been known for a long time, an aluminum-rich phase A1_4B_xC_4 with variable boron content (.v = 1 -3) was first reported in 1964. Later thecomposition A1_8B_4C_7 was proposed without data on a crystal structure of the compound. A detailed characterization was thus desirable, because tins phase plays an important role in the investigation of hard materials ("cermets") based on boron carbide"B_4C" and aluminum. The structure analysis of single crystals, which were obtained from the synthesis in molten aluminum, showed that the correct composition is Al_3BC_3, that is a Carbidecarboborate of aluminum. Vibratioriai spectra confirm that the linear CBC group in Al_3BC_3 can be formulated as a complex union (C=B=C)~(5-) and thus represents the id-electron system isoelectronit to CO_2 with the highest neuative charae.