Single crystals of tris(2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepin-1-ium) tri-μ2-iodido-bis[triiodidobismuth(III)], (C9H17N2)3[Bi2I9], were prepared by a solvothermal method, heating a mixture of BiI3, KI, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and ethanol at 443 K for six days. The asymmetric unit of the title compound, which crystallizes in the monoclinic space group P21/c, contains one [Bi2I9]3− anion and three protonated DBUH+ moieties. The dinuclear [Bi2I9]3− anions, which are composed of face-sharing BiI6 3− octahedra, are packed in columns parallel to the [010] direction, and separated by protonated DBUH+ moieties. The optical band gap of (C9H7N2)3Bi2I9 is 2.1 eV.

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