Si₆ , Si₁₄ , and Si₂₂ Rings in Iodide Silicides of Rare Earth Metals

A new class of compounds containing layers of Si_n Zintl polyanions is represented by the silicides MISi (M=La, Ce, Pr), La₄ I₃ Si₄ , and La₅ I₃ Si₅ (a section of the structure is shown below). Their structures contain Si₆ and the previously unknown Si₁₄ and Si₂₂ rings, which are condensed into layers. The Si atoms are coordinated in a trigonal-prismatic fashion by M atoms to give M-(SiSi)-M slabs that are bonded to one another through I atoms. An extensive chemistry of halide silicides similar to that of the carbide halides of the rare earth metals can be expected.