Halogen bonds regulating structures and optical properties of hybrid iodobismuthate perovskites

摘要

Successive structural transformations were observed in a methanolic solution containing 4-iodo-1methylpyridin-1-ium iodide (IPyMe.I) and bismuth iodide (BiI3). When kept in the solution, the amorphous solid (P_1) obtained immediately on mixing would transform to needle crystals (C_1) in hours, which would convert to prismatic crystals (C_2) in around 2 days. In the presence of hydroiodic acid, the hydro thermal reaction of IPyMe.I and BiI3 also gave rise to C_2, and crystals of C_2 in this solution would transform to a third crystalline product C_3 in ca. 3 days. X-ray single crystal diffraction experiments show C_1 containing one-dimensional {BiI4-}(n) chains, C_2 as a binuclear Bi2I93- structure, and C_3 consisting of a monomeric BiI63- unit, all with IPyMe+ as counter cations. Halogen bonds exist between IPyMe+ and the iodobismuthate, which may play key roles in the structural transformation. By introducing halogen bonding, the hybrids demonstrate excellent water-resistance. A thermal-induced reversible colour change from yellow to dark red occurred from 100 K to 450 K for all three hybrids, in which lattice expansion over the temperature range may be a reason for the thermochromism. The bandgaps derived from the UV-vis diffusion reflectance for the three complexes were 1.80 eV for C_1, 1.84 eV for C_2 and 2.00 eV for C_3. DTF computations followed by electron density topological analysis were applied to explain the structure-optical property relationship for complexes of diverse iodobismuthate types but the same counter cation. It was found that the nature of the Bi-I bonds rather than the dimensionality of the inorganic iodobismuthates is mainly responsible for the light absorption of the materials.

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