posted on 2002-03-27, 00:00authored byDavid B. Mitzi, David R. Medeiros, Patrick R. L. Malenfant
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.