Heike Haller

Structural Proof for a Higher Polybromide Monoanion: Investigation of [N(C3H7)4][Br9]

The chemistry of polyhalides, especially of polyiodides, has long been known. 2] The first systematic investigation of these anions goes back to Jçrgensen in 1870. Since these pioneering years, a great variety, mainly of polyiodides, have been investigated. The lighter and more reactive halogens, bromine, chlorine, and fluorine, have been less explored which is probably due to the relative ease of handling iodine. However, in the past year, the investigation of lighter polyhalides has once again come into the focus of the scientific community. Feldmann et al. have reported the preparation of a 3D polybromide network [C4MPyr]2[Br20] [7] in ionic liquids. A series of tetraethylammonium polybromides was also investigated by Raman spectroscopy. Moreover, the first free trifluoride monoanion was characterized by matrix-isolation spectroscopy under cryogenic conditions in argon and neon matrices. All these recent reports indicate that our knowledge of polyhalides is still relatively limited and provides room for new discoveries. The chemistry of polybromides is especially limited compared to the extensive chemistry of polyiodides. Among the polybromide monoanions, only the [Br3] anion was fully characterized, including single-crystal X-ray diffraction. All other known polybromide monoanions (penta, hepta, and nona) were only characterized by IR and/or Raman spectroscopy. Based on these data, their structures were only tentatively assigned. High level quantum-chemical calculations, which could support the structure assignment based on vibrational data for the nonabromide have not been performed. Only calculations at the HF level have been carried out but these do not provide definitive information because of the lack of electron correlation. By far the most prominent polybromides are dianions, such as [Br8] 2 , [Br10] 2 , and [Br20] 2 [7] or polybromide networks 14–16] [{Br3} ·=2 Br2], and [(Br )2·3 Br2]. These compounds are not only of academic interest, they can be used for many practical applications such as zinc–bromine batteries, 18] water treatment, or selective bromination reactions. Furthermore, an application as redox couple in dyesensitized solar cells (DSSC) is promising, a field which is a more and more important in energy generation. Herein, we report the first synthesis of the nonabromide salt [NPr4][Br9]. The reaction of tetrapropylammonium bromide and excess bromine leads to the formation of brownish red crystals. These crystals are relatively stable and can even be handled briefly in air. The single-crystal X-ray structure determination shows that the salt [NPr4][Br9], crystallizes in the tetragonal space group I 4, Figure 1. Similar to other known polyhalides, the [Br9] structure is based on a central bromide anion Br ,

Polychloride monoanions from [Cl3]- to [Cl9]- : a Raman spectroscopic and quantum chemical investigation.

Polychloride monoanions stabilized by quaternary ammonium salts are investigated using Raman spectroscopy and state-of-the-art quantum-chemical calculations. A regular V-shaped pentachloride is characterized for the [N(Me)(4)][Cl(5)] salt, whereas a hockey-stick-like structure is tentatively assigned for [N(Et)(4)][Cl(2)⋅⋅⋅Cl(3)(-)]. Increasing the size of the cation to the quaternary ammonium salts [NPr(4)](+) and [NBu(4)](+) leads to the formation of the [Cl(3)](-) anion. The latter is found to be a pale yellow liquid at about 40 °C, whereas all the other compounds exist as powders. Further to these observations, the novel [Cl(9)](-) anion is characterized by low-temperature Raman spectroscopy in conjunction with quantum-chemical calculations.

A 2D Polychloride Network Held Together by Halogen–Halogen Interactions

In a eutectic mixture of two ionic liquids, we have synthesized and crystallized the new polychloride compound [Et4 N]2 [(Cl3 )2 ⋅Cl2 ] that exhibits a periodic 2D polychloride network acting as an anionic layer. Based on its low melting point and vapor pressure, this compound can be described as a room-temperature ionic liquid. The compound was fully characterized by IR and Raman spectroscopy as well as single-crystal X-ray structure determination. The characterization was complemented by solid-state quantum-chemical calculations confirming the results of the experimental work.

[HMIM][Br9]: a Room-temperature Ionic Liquid Based on a Polybromide Anion

[HMIM][Br9] ([HMIM]=1-hexyl-3-methylimidazolium) has been investigated by Raman spectroscopy, single-crystal X-ray diffraction and NMR spectroscopy. Conductivity measurements show a high electrical conductivity like other polybromides. Graphical Abstract [HMIM][Br9]: a Room-temperature Ionic Liquid Based on a Polybromide Anion