LiB12PC, the first boron-rich metal boride with phosphorus--synthesis, crystal structure, hardness, spectroscopic investigations |
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Authors: | Vojteer Natascha Sagawe Vanessa Stauffer Julia Schroeder Melanie Hillebrecht Harald |
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Affiliation: | Institut für Anorganische und Analytische Chemie, Albertstr. 21, 79104 Freiburg, Germany. |
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Abstract: | We present synthesis, crystal structure, hardness, and IR/Raman and UV/Vis spectra of a new compound with the mean composition LiB12PC. Transparent single crystals were synthesised from Ga, Li, B, red phosphorus and C at 1500 °C in boron nitride crucibles welded in Ta ampoules. Depending on the type of boron used for the synthesis we obtained colourless, brown and red single crystals with slightly different P/C ratios. Colourless LiB12PC crystallizes orthorhombic in the space group Imma (No. 74) with a=10.188(2) Å, b=5.7689(11) Å, c=8.127(2) Å and Z=4. Brown LiB12P0.89C1.11 is very similar, but with a lower P content. Red single crystals of LiB12P1.13C0.87 have a larger unit cell with a=10.4097(18) Å, b=5.9029(7) Å, c=8.2044(12) Å. EDX measurements confirm that the red crystals contain more phosphorus than the other ones. The crystal structure is characterized by a covalent network of B12 icosahedra connected by exohedral B? B bonds and P? P, P? C or C? C units. Li atoms are located in interstitials. The structure is closely related to MgB7, LiB13C2 and ScB13C. LiB12PC fulfils the electron counting rules of Wade and also Longuet‐Higgins. Measurements of Vickers micro‐hardness (HV=27 GPa) revealed that LiB12PC is a hard material. The optical band gaps obtained from UV/Vis spectra match the colours of the crystals. Furthermore we report on the IR and Raman spectra. |
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Keywords: | boron crystal growth lithium phosphorus structure elucidation |
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