Effect of Mono- versus Di-ammonium Cation of 2,2‘-Bithiophene Derivatives on the Structure of Organic−Inorganic Hybrid Materials Based on Iodo Metallates

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Abstract
2,2‘-bithiophene derivatives, 5-ammoniumethylsulfanyl-2,2‘-bithiophene (AESBT) and 5,5‘-bis(ammoniumethylsulfanyl)-2,2‘-bithiophene (BAESBT), have been designed for their incorporation in organic−inorganic materials based on iodometalates. Three layered compounds, (BAESBT)PbI4, (AESBT)4Pb3I10, and (AESBT)3Bi2I9, have been synthesized as crystals from slowly cooled aqueous solution containing metal halide and bithiophene derivative salts. When starting from the diammonium cation, (BAESBT)PbI4 hybrid perovskite is obtained. (BAESBT)PbI4 adopts a triclinic cell (P1̄) with the lattice parameters a = 8.4741(5) Å, b = 8.9255(6) Å, c = 16.876(1) Å, α = 88.328(5)°, β = 81.806(4)°, γ = 88.864(5)°, Z = 2. In the structure, PbI42- perovskite sheets and diammonium cation layers alternate along c. The incorporation of the corresponding monoammonium cation (AESBT) leads to a head to tail arrangement of the molecules in the (AESBT)4Pb3I10 hybrid, precluding the formation of the perovskite layers. (AESBT)4Pb3I10 is orthorhombic, Pna21, with a = 38.333(4) Å, b = 22.239(3) Å, c = 8.448(2) Å, Z = 4. The structure consists of corrugated layers of Pb3I104- separated by organic layers of monoammonium cations. A similar relative situation of molecules in organic layers is observed in (AESBT)3Bi2I9, with the inorganic sheets being built up from Bi2I93- entities. (AESBT)3Bi2I9 crystallizes in an orthorhombic cell (P212121) with a = 8.4564(6) Å, b = 21.368(2) Å, c = 30.747(2) Å, Z = 4. In the three compounds, the molecular packings appear different, underlining the interplay between both organic and inorganic components. New packings are stabilized, as illustrated by an original mixed kappa−alpha type arrangement of the bithiophene units in (AESBT)3Bi2I9. Furthermore, molecular interactions, especially of S...S type, appear stronger in the hybrids based on the monoammonium cations. The electrical conductivity of a (BAESBT)PbI4 single crystal has also been investigated, revealing a semiconductive behavior with a characteristic energy of Eg = 2.535 eV.