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.