Solid state anion–π interactions involving polyhalides

Abstract

The stabilization of polyhalides in the solid state with the support of electron-deficient pentafluorophenyl groups is described. Furthermore, a synthetic approach towards the sensitive tetraiodide dianion is described and ESI mass spectrometric evidence for its presence in solution is reported.

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX3 (X = Br, I)

“…This is an X 2 charge transfer complex with the two nearest crystal halides, stabilized by π‐anion interactions with the four nearest FA cations. Such π‐anion interactions are known to stabilize X 4 2− ‐complexes in macromolecules and solids with structural match for caging them . Interestingly, Int I +1 with the linear symmetrical I 3 − ‐complex, see Figure S6 (Supporting Information), described as most representative for MAPbI 3 , is 211 meV higher in energy.…”

“…To study X-migrations in α-FAPbX 3 we consider a halogen vacancy (V X ) and a halogen interstitial (Int X ) in −1 and +1 charged states (V X −1, V X +1, Int X −1, Int X +1), using 3 × 3 × 3 supercells, as well as a halogen molecular interstitial (Int X2 ), using a 4 × 3 × 3 supercell, see Figure 3. [47][48][49][50] Interestingly, Int I +1 with the linear symmetrical I 3 − -complex, see Figure S6 (Supporting Information), described as most representative for MAPbI 3 , [15,16,46,51] is 211 meV higher in energy. [45] Recently, it was stated for V I −1 in MAPbI 3 that the PbPb dimer is not the energy minimum due to spin-orbit coupling.…”

“…Such π-anion interactions are known to stabilize X 4 2− -complexes in macromolecules and solids with structural match for caging them. [47][48][49][50] Interestingly, Int I +1 with the linear symmetrical I 3 − -complex, see Figure S6 (Supporting Information), described as most representative for MAPbI 3 , [15,16,46,51] is 211 meV higher in energy. We find that Int X2 also causes formation of a [X···X 2 ···X] 2− -complex with XX bond of 2.57 and 2.98 Å length, X···X 2 bond of 2.95, 3.03 and 3.22, 3.49 Å length.…”

Anion−π Interactions with Fluoroarenes

“…121,123,124 The crystal structure of the interhalide Br−I−Br − is a starting point for extended studies of anion−π interactions of C 6 F 5 units with poly-and interhalides, 126 , and BrIBr − as counterion has been synthesized ( Figure 39). 127 By crystallization of pentafluorobenzyl quinolinium hydrobromide in the presence of air, the simple bromide as well as the tribromide structure 23 is obtained (Figure 40). While the bromide shows anion−π contacts with only one carbon atom of the C 6 F 5 unit (η 1 -type; C···Br = 3.88 Å), the slightly asymmetric tribromide salt (Br 1 −Br 2 = 2.64 Å, Br 2 −Br 3 = 2.47 Å) exhibits an interesting porous structure, where the linear polyhalide is paneled by C 6 F 5 at the ends (η 3 -type, C··· Br 1 = 3.60−3.02 Å; η 6 -type, C···Br 1 = 3.43−4.02 Å) and quinolinium is positioned at the flanks (C···Br 2 = 3.67 Å, N··· Br 1 = 3.62 Å).…”

Molecular self-assembly of 1D infinite polyiodide helices in a phenanthrolinium salt

“…1 Structures of larger bulky polyiodides are stabilized by various intermolecular interactions within a crystal, such as hydrogen bond, electrostatic halogen-halogen, anion⋯π, and dispersion interactions. [2][3][4][5][6] Generally, the bigger cations allow for the formation of longer stable polyiodide chains in the solid state. 7 Additionally, the cation shape and its polarizability play an important role in the final length and geometry of the polyiodide anion.…”