Novel Compounds Sn 10In 14P 22I 8 and Sn 14In 10P 21.2I 8 with Clathrate I Structure: Synthesis and Crystal and Electronic Structure

Two new supramolecular pnictidehalides Sn₁₀In₁₄P₂₂I₈ (I) and Sn₁₄In₁₀P_21.2I₈ (II) have been synthesized using a standard ampoule technique. Both compounds possess the clathrate I type of structure. I crystallizes in the cubic space group Pmoverline3n (No. 223) with the unit cell parameter a=11.0450(7) Å (Z=1) while II reveals a complicated superstructure (space group P4₂/m (No. 84), a=24.745(3) Å, c=11.067(1) Å, Z=5) resulting from the partial ordering of vacancies at phosphorus sites. The crystal structures have been solved based on single-crystal X-ray diffraction data sets (ω-2θ scans, least-squares refinement against F²) to R=0.0376 (Sn₁₀In₁₄P₂₂I₈) and R=0.0569 (Sn₁₄In₁₀P_21.2I₈). In both structures metal and phosphorus atoms form a cationic clathrate I framework hosting iodine atoms in the cavities. The composition of both phases complies with the Zintl-Klemm formalism which justifies the existence of vacancies in the structure of II. The ¹¹⁹Sn Mössbauer spectroscopy data together with the results of the band structure calculations suggest that the electron density on tin atoms is reduced in favor of bands, which lie just below the Fermi level and must define electronic properties of the compounds in question. The differences in the crystal and electronic structures of the cationic tin clathrates are discussed.