Iodide and triiodide anion complexes involving anion–π interactions with a tetrazine-based receptor

Abstract

Protonated forms of the tetrazine ligand L2 (3,6-bis(morpholin-4-ylethyl)-1,2,4,5-tetrazine) interact with iodide in aqueous solution forming relatively stable complexes (ΔG° = -11.6(4) kJ mol for HL2 + I = (HL2)I and ΔG° = -13.4(2) kJ mol for HL2 + I = [(HL2)I]). When solutions of [(HL2)I] are left in contact with air, crystals of the oxidation product (HL2)(I)I·4HO are formed. Unfortunately, the low solubility of I complexes prevents the determination of their stability constants. The crystal structures of HL2I·HO (1), HL2(I)·2HO (2) and (HL2)(I)I·4HO (3) were determined by means of X-ray diffraction analyses. In all crystal structures, it was found that the interaction between I and I with HL2 is dominated by anion interactions with the π electron density of the receptor. Only in the case of 1, the iodide anions involved in close anion-π interactions with the ligand tetrazine ring form an additional H-bond with the protonated morpholine nitrogen of an adjacent ligand molecule. Conversely, in crystals of 2 and 3 there are alternate segregated planes which contain only protonated ligands hydrogen-bonded to cocrystallized water molecules or I and I forming infinite two-dimensional networks established through short interhalogen contacts, making these crystalline products good candidates to behave as solid conductors. In the solid complexes, the triiodide anion displays both end-on and side-on interaction modes with the tetrazine ring, in agreement with density functional theory calculations indicating a preference for the alignment of the I molecular axis with the molecular axis of the ligand. Further information about geometries and structures of triiodide anions in 2 and 3 was acquired by the analysis of their Raman spectra.

Perovskite Solar Cells: From the Laboratory to the Assembly Line

“…The fabrication of cheap and large‐area PSCs in also fundamental for the design of energy conversion/storage integrated devices, especially when PSCs should recharge batteries or supercapacitors . More broadly, photovoltaics is the ideal interface for many current technologies …”

“…[148][149][150][151] More broadly,p hotovoltaics is the ideal interface for many current technologies. [152][153][154][155][156][157][158][159][160][161]…”

Iodide···π Interactions of Perhalogenated Quinoid Rings in Co-crystals with Organic Bases

“…8 A close contact with an anion or a lone electron pair is possible for electron-depleted rings and a number of such interactions have been documented. [9][10][11][12][13][14][15][16] Unlike aromatics, which are mostly electron-rich (except those with five or six electronwithdrawing substituents), quinoid rings are inherently electron-poor due to a lack of electron delocalization and the presence of carbonyl groups; they can be further depleted by introduction of electronegative substituents. Perhalogenoquinones act as mild oxidants and can easily be reduced into semiquinone radicals by mild reducing agents such as iodide ions.…”

Stabilization of Supramolecular Networks of Polyiodides with Protonated Small Tetra-azacyclophanes

“…Moreover, polyiodide systems have recently encountered a broad technological interest, mainly connected with solar energy harvesting and storage, e.g., dye-sensitized solar cells and batteries, where they have been successfully implemented as electrolyte in various forms [12,13]. Solid-state conductors based on the Grotthus conduction mechanism [3,14] are also a major field of research [15][16][17]; on this side some of us recently reported about the possibility of using supramolecular forces, such as the strong anion-π interactions exerted by s-tetrazines [18], to direct the assembly of polyiodide networks [19].…”