Some phosphide halides of lanthanum and related compounds

The pnictide halides La2I2P, La2I2As, La2I2Sb, La2Br2P and Y2Br2P have been synthesized from lanthanum and yttrium, red phosphorus, arsenic, and antimony, respectively, and the corresponding metal trihalides. Their structures contain close-packed metal atom double layers with pnicogen atoms in the octahedral voids. These layers are sandwiched by halogen atom layers. The compounds crystallize in the trigonal I T-type with one sandwich-like layer per unit cell, or in the rhombohedral 3R-type with three layers per unit cell. Polytypism and twinning have been observed. For 3R-La2I2P, conductivity measurements have shown metallic behaviour.