Novel compounds Sn10In14P22I8 and Sn14In10P21.2I8 with clathrate I structure: Synthesis and crystal and electronic structure

Two new supramolecular pnictidehalides Sn10In14P22I8 (I) anti Sn14In10P21.2 I8 (II) have been synthesized using a standard ampoule technique. Both comp ounds possess the clathrate I type of structure. I crystallizes in the cubi c space group Pm (3) over barn (No. 223) with the unit cell parameter a = 1 1.0450(7) (Z = 1) while II reveals a complicated superstructure (space grou p P4(2)/m (No. 84), a = 24.745(3) Angstrom, c = 11.067(1) Angstrom, Z = 5) resulting from the partial ordering of vacancies at phosphorus sites. The c rystal structures have been solved based on single-crystal X-ray diffractio n data sets (omega -2 theta) scans, least-squares refinement against F-2) t o R = 0.0376 (Sn10In14P22I8) and R = 0.0569 (Sn14In10P21.2I8). In both stru ctures metal anti phosphorus atoms form a cationic clathrate I framework ho sting 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 Sn-119 Mossbauer spectroscopy data together wit h 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 ques tion. The differences in the crystal and electronic structures of the catio nic tin clathrates are discussed. (C) 2001 Academic Press.