PLANAR B-4 RHOMBOIDS - THE RARE-EARTH BOLIDE HALIDES RE4X5B4

The new compounds RE4X5B4 (RE = La, Ce, Pr, Gd and X = Br, I) and RE4I 5B2C (RE = La, Ce) are prepared via the reaction of RE metal, REX3 and B, or B and C at temperatures 1670 greater than or equal to T greater than or equal to 1270 K in welded tantalum ampoules. Chains of interc onnected B-4 rhomboids are the characteristic features of the crystal structures. According to band structure calculations, the compounds ar e one-dimensional metals which undergo a gradual metal-to-semiconducto r transition at low temperature as experimentally indicated by the ste ep inrease of electrical resistivity.