Intercalated Organic−Inorganic Perovskites Stabilized by Fluoroaryl−Aryl Interactions

Abstract

Crystals of several new hybrid tin(II) iodide-based perovskites, involving 2,3,4,5,6- pentafluorophenethylammonium or phenethylammonium cation bilayers and intercalated aryl or perfluoroaryl molecules, were grown by slow evaporation of a methanol solution containing the hybrid perovskite and the intercalating species. The (C₆F₅C₂H₄NH₃)₂SnI₄·(C₆H₆) structure was solved at −75 °C in a monoclinic C2/c subcell [a = 41.089(12) Å, b = 6.134(2) Å, c = 12.245(3) Å, β = 94.021(5)°, Z = 4] and consists of sheets of corner-sharing distorted SnI₆ octahedra separated by bilayers of pentafluorophenethylammonium cations. The intercalated benzene molecules form a single well-ordered layer interposed between adjacent fluoroaryl cation layers. The corresponding hybrid with an unfluorinated organic cation and fluorinated intercalating molecule, (C₆H₅C₂H₄NH₃)₂SnI₄·(C₆F₆), is isostructural [a = 40.685(4) Å, b = 6.0804(6) Å, c = 12.163(1) Å, β = 93.136(2)°, Z = 4]. For each intercalated system, close C···C contacts (3.44−3.50 Å) between the aromatic cation and the intercalated molecule are indicative of a significant face-to-face interaction, similar to that found in the complex C₆H₆·C₆F₆. Crystal growth runs with the organic cation and prospective intercalating molecule either both fluorinated or both unfluorinated did not yield stable intercalated compounds, demonstrating the significance of fluoroaryl−aryl interactions in the current intercalated structures. Thermal analysis of (C₆F₅C₂H₄NH₃)₂SnI₄·(C₆H₆) and (C₆H₅C₂H₄NH₃)₂SnI₄·(C₆F₆) crystals yields, in addition to the characteristic transitions of the parent perovskite, endothermic transitions [12.6(5) and 32.1(8) kJ/mol, respectively] with an onset at 145 °C and a weight loss corresponding to the complete loss of the intercalated molecule. The relatively high deintercalation temperature (well above the boiling point of benzene and hexafluorobenzene) demonstrates the usefulness of the hybrid perovskites in providing a stable framework for the examination of the fluoroaryl−aryl interaction, as well as the potential importance of this interaction in tailoring new hybrid perovskites. UV−vis absorption measurements on (C₆H₅C₂H₄NH₃)₂SnI₄·(C₆F₆) thin films indicate a small reversible wavelength shift to higher energy for the tin(II) iodide framework exciton peak (with respect to that of the parent perovskite spectrum), from 608(2) nm [2.04 eV] to 595(2) nm [2.08 eV], and a corresponding shift in the band edge position. This spectral shift can most reasonably be attributed to subtle structural changes induced in the tin(II) iodide sheets by the intercalated hexafluorobenzene molecules.