Hybrid bismuth-containing halides are emerging as alternative candidates to lead-containing perovskites for light-harvesting applications, as Bi 3 + is isoelectronic with Pb 2 + and the presence of an active lone pair of electrons is expected to result in outstanding charge-carrier transport properties. Here, we report a family of one binary and three ternary iodobismuthates containing 1,4-diazabicyclo[2.2.2]octane (DABCO). These materials have been prepared solvothermally and their crystal structures, thermal stability, and optical properties determined. Reactions carried out in the presence of bismuth iodide and DABCO produced (C 6 H 12 N 2 )BiI 3 ( 1 ), which consists of hybrid ribbons in which pairs of edge-sharing bismuth octahedra are linked by DABCO ligands. Short I···I contacts give rise to a three-dimensional network. Similar reactions in the presence of copper iodide produced (C 8 H 17 N 2 ) 2 Bi 2 Cu 2 I 10 (2) and [(C 6 H 13 N 2 ) 2 BiCu 2 I 7 ](C 2 H 5 OH) (3) in which either ethylated DABCO cations (EtDABCO) + or monoprotonated DABCO cations (DABCOH) + are coordinated to copper in discrete tetranuclear and trinuclear clusters, respectively. In the presence of potassium iodide, a unique three-dimensional framework, (C 6 H 14 N 2 )[(C 6 H 12 N 2 )KBiI 6 ] (4) , was formed, which contains one-dimensional hexagonal channels approximately 6 Å in diameter. The optical band gaps of these materials, which are semiconductors, range between 1.82 and 2.27 eV, with the lowest values found for the copper-containing discrete clusters. Preliminary results on the preparation of thin films are presented.
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.
Two new hybrid iodobismuthates, [C8H17N2][C10H22N2][BiI6] (1) and [C6H12N2]0.5[C10H22N2]3.5[Bi2I10][Bi2I9] (2), have been prepared by solvothermal synthesis in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) and ethanol. Both compounds have been characterized by single-crystal and powder X-ray diffraction, infrared and UV–Vis spectroscopies and thermogravimetric analysis. Structure determination reveals that the crystal structure of 1 contains mononuclear [BiI6]3− anions, whilst 2 contains an unusual combination of dinuclear anions, [Bi2I9]3− and [Bi2I10]4−, consisting of two edge- and two face-sharing [BiI6]3− octahedra, respectively. Mono- and diethylated derivatives of DABCO, which are formed in situ under solvothermal conditions, act as countercations and are located between the discrete anions. The optical band gaps of 1 and 2, which are 2.29(1) and 2.03(2) eV respectively, are consistent with the red color of these compounds, and are comparable to the band gaps measured for other iodobismuthates containing discrete anions. Graphical Abstract Two new iodobismuthates, [C8H17N2][C10H22N2][BiI6] (1) and [C6H12N2]0.5[C10H22N2]3.5[Bi2I10][Bi2I9] (2), have been synthesized under solvothermal conditions, and their crystal structures determined by single-crystal X-ray diffraction.
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