Planar B₄ Rhomboids: The Rare Earth Boride Halides RE₄X₅B₄

The new compounds RE4X5B4(RE)La, Ce, Pr, Gd and X)Br, I) and RE4I5B2C RE)La, Ce) are prepared via the reaction of RE metal, REX3and B, or B and C at temperatures 1670gTg 1270 K in welded tantalum ampoules. Chains of interconnected B4 rhomboids are the characteristic features of the crystal structures. According to band structure calculations, the compounds are one-dimensional metals which undergo a gradual metal-to-semiconductor transition at low temperature as experimentally indicated by the steep inrease of electrical resistivity