Crystal structure of (C₉H₁₇N₂)₃[Bi₂I₉]

Single crystals of tris-(2,3,4,6,7,8,9,10-octa-hydro-pyrimido[1,2-a]azepin-1-ium) tri-μ₂-iodido-bis-[tri-iodido-bis-muth(III)], (C₉H₁₇N₂)₃[Bi₂I₉], were prepared by a solvothermal method, heating a mixture of BiI₃, KI, 1,8-di-aza-bicyclo-[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- octa-hedra, 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.