Crystals of formamidinium antimony, halides, FA3Sb2X9 FA = CH (NH2) 2+; X = Br- and I- or triformamidinium nonahalidodiantimony, (CH5N2) 3Sb2X9, 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. FA3Sb2Br9 belongs to the trigonal space group P3m1, which is known as the Cs3Bi2Br9 structure type, and FA3Sb2I9 belongs to the hexagonal space group P63/mmc, called the Cs3Cr2Cl9 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.
Bhatt et al. (Wed,) studied this question.