Synthesis and Characterization of Li‐containing Boron Carbide r‐Li~1B13C2. Issue 3 (7th October 2018)

• Record Type: Journal Article
• Authors: Hillebrecht, Harald; Vojteer, Natascha; Sagawe, Vanessa; Hofmann, Kathrin; Albert, Barbara
• Is Part Of: Zeitschrift für anorganische und allgemeine Chemie. Volume 645:Issue 3(2019)
• Page Start: 362
• Page End: 369
• Publication Date: 2018-10-07
• Subjects: Boron‐rich boride -- Boron carbide -- Wade's rules -- Bader charges -- Structure elucidation; Chemistry, Inorganic -- Periodicals; Chemistry -- Periodicals; 540
• DOI: 10.1002/zaac.201800289
• Languages: English
• ISSNs: 0044-2313

Abstract

Abstract : Transparent and nearly colorless single crystals of r ‐LiB13 C2 were obtained by reaction of boron with Li2 CO3 in a Cu melt at 1250–1300 °C. The structure analysis [ R 3 m, a = 5.6535(1), c = 12.5320(2) Å, 421 independent reflections, 22 parameters, R 1 = 0.034, wR 2 = 0.093] revealed a crystal structure that can be described as a filling variant of rhombohedral B13 C2 . Li + is located in a void above or below the linear CBC unit. The site occupation is close to 50 % resulting in an electron‐precise composition according to Wade's rules if a positive charge is given to the CBC entity: Li + (B12 ) 2– (CBC) + . The displacement parameters of the CBC unit indicate disorder in the [001] direction, that relates to the short Li–C distance and the partial occupation of the Li + site. The composition is confirmed by EELS measurements of single crystals. Band gap calculations give a value of 2.94 eV, which is in agreement to the crystals being colorless. The evaluation of the electron density by application of the QTAIM formalism as proposed by Bader modifies the assignment pictured above according to Wade's rules. In agreement to the electronegativities the carbon atoms carry a negative charge (–2.31/–2.42) and the effective charges are: Li +0.81 (B12 ) +2.02 (CBC) –2.83 . Abstract :