Caesium enneabromodibismuthate is an inorganic compound with the formula Cs3Bi2Br9.

It is one of the coordination complexes formed by caesium, bismuth and bromine.

[1] At room temperature, it is trigonal (P3m1) and it undergoes phase transformation to monoclinic phase (C12/c1) when the temperature is below 96 K.[2] Traditionally, it can be synthesized from a hydrobromic acid solution of stoichiometric amounts of caesium bromide and bismuth hydroxide or bismuth(III) oxide,[3] crystals are formed by cooling the hot, saturated solution.

[4] It can also be obtained by reacting caesium bromide and bismuth(III) bromide in DMF, followed by vaporizing the solvent.

[5] Its nanocrystals can be synthesized in 1-octadecene at 170 °C using caesium oleate and bismuth(III) bromide as precursors.