Room-temperature crystal structures of [CH(NH 2 ) 2 ] 3 Sb 2 X 9 ( X = Br and I)

Crystals of formamidinium antimony, halides, FA 3 Sb 2 X 9 {FA = [CH(NH 2 ) 2 ] + ; X = Br − and I − } {or triformamidinium nonahalidodiantimony, (CH 5 N 2 ) 3 [Sb 2 X 9 ]}, have been synthesized using a counter diffusion crystal growth (CDCG) method in silica gel and their structures determined from single-crystal X-ray diffraction data. FA 3 Sb 2 Br 9 belongs to the trigonal space group P 3 m 1, which is known as the Cs 3 Bi 2 Br 9 structure type, and FA 3 Sb 2 I 9 belongs to the hexagonal space group P 6 3 / mmc , called the Cs 3 Cr 2 Cl 9 structure type. The change of the anion type from bromide to iodide results in the change of the structure type and the connectivity of the Sb— X octahedra. These structures are described and compared to the crystal types known for vacancy-ordered triple-perovskites.