Planar B4 rhomboids: The rare earth boride halides RE4X5B4

Article abstract of DOI:10.1021/jp971500q

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, REX₃ and B, or B and C at temperatures 1670 ≥ T ≥ 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.