Ionic liquids (IL) are valuable in a variety of applications due to their high electrochemical stability and physical properties. Using the cation 1-methyl-3-octylimidazolium, [OMIM]+, the bromidostannate RTIL [OMIM][Sn+IIBr3], "undercooled melt" [OMIM][Sn+IVBr5], and IL [OMIM]2[Sn+IVBr6] were synthesized. The uncommon solid state structure of [SnBr5]- was elucidated in the form of its RTIL salt. Additionally, the IL based on tribromine-monoanion [OMIM][Br3] was used to dissolve metallic Sn, selectively resulting in the formation of [SnBr3]- as confirmed by Raman spectroscopy. Subsequent cyclic voltammograms (CV) of [SnBr3]- confirmed the deposition potential of metallic Sn and renewal of the polybromide [Br3]-. The RTIL bromidostannates were stable compounds, making a selective electrochemical investigation of the deposition of metallic Sn(0) to Sn(+II)/Sn(+IV) redox process possible, via conductance and CV measurements. The CVs of the RTILs and of solutions in propylene carbonate had the redox couples of Sn(0)/[Sn+IIBr3]-/[Sn+IVBr5]-.
So far, several publications have discussed the bonding concepts in polyhalides on a theoretical basis. In particular, the trichlorine monoanion is of great interest because its structure should be symmetrical and show two equidistant Cl-Cl bonds. However, apart from matrix-isolation studies, only asymmetric trichlorine anions have been reported so far. Herein, the trichlorine monoanions in 2-chloroethyltrimethylammonium trichloride [NMe3 EtCl][Cl3 ], 1, tetramethylammonium trichloride [NMe4 ][Cl3 ], 2, and tetrapropylammonium trichloride [NnPr4 ][Cl3 ], 3, are analysed. High-resolution X-ray structures and experimental charge density analyses supported by periodic quantum-chemical calculations provide insight into the influence of the crystalline environment on the structure of these [Cl3 ]- anions as well as into the progress of the bond formation between a dichlorine molecule and a Cl- anion.
Trifluoromethylation of [AuF3 (SIMes)] with the Ruppert-Prakash reagent TMSCF3 in the presence of CsF yields the product series [Au(CF3 )x F3-x (SIMes)] (x=1-3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the 19 Fâ NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of trans-[Au(CF3 )F2 (SIMes)] and [Au(CF3 )3 (SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the 13 Câ NMR spectrum reveals that trans-[Au(CF3 )F2 (SIMes)] and [Au(CF3 )3 (SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the Au-Ccarbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13 Câ NMR spectrum is presented.
The use of neat BrCl in organic and inorganic chemistry is limited due to its gaseous aggregate state and especially its decomposition into Cl2 and Br2 . The stabilization of BrCl in form of reactive ionic liquids via a novel in situ synthesis route shifts this equilibrium drastically to the BrCl side, which leads to safer and easier-to-handle interhalogenation reagents. Furthermore, the crystalline derivatives of the hitherto unknown [Cl(BrCl)2 ]- and [Cl(BrCl)4 ]- anions were synthesized and characterized by single-crystal X-ray diffraction (XRD), Raman and IR spectroscopy, as well as quantum chemical calculations.
This Review deals with the evolving field of polyhalogen chemistry, specifically polyhalogen anions (polyhalides). In addition to a historical outline, current progress in synthetic approaches towards the formation of polyfluorides, polychlorides, polybromides, and polyinterhalides is also illustrated. The structural diversity of polyhalides has substantially increased in the past decade, especially for polychlorides and polybromides, which are commonly characterized by single-crystal X-ray diffraction, Raman spectroscopy, and quantum-chemical calculations. Polyfluorides have been examined by sophisticated state-of-the-art quantum-chemical calculations and investigated spectroscopically in noble gas matrix-isolation experiments under cryogenic conditions at 4â K. The bonding in such polyhalide systems is also discussed. The last Section deals with applications of polyhalides in halogenation reactions and electrochemistry as well as their use as reactive ionic liquids, emphasizing the promising future of polyhalogen chemistry.
Pseudohalogens are defined as molecular entities that resemble the halogens in their chemistry. While our understanding of polyhalogen chemistry has increased over the last years, research on polypseudohalogen compounds is lacking. The pseudohalogen BrCN possesses a highly pronounced σ-hole at the bromine side of the molecule, inducing strong halogen bonding. This allows the synthesis and characterization of new polypseudohalogen anions, as shown by the single-crystal X-ray diffraction of [PNP][Br(BrCN)] and [PNP][Br(BrCN)3 ]. Both the nearly linear anion [Br(BrCN)]- and the distorted pyramidal anion [Br(BrCN)3 ]- were characterized by Raman spectroscopy and quantum-chemical calculations. The behavior of the polypseudohalogen compounds in solution and as room-temperature ionic liquids (RT-ILs) using the [NBu4 ]+ cation was studied by 13 C and 15 N NMR spectroscopy. These types of ILs are capable of dissolving elemental gold and offer themselves as promising compounds in metal recycling.
Due to a more distinct σ-hole, BrCl is able to form stronger halogen bonds than those in polyhalogen anions based on Cl2 and Br2 . This stabilization allows the crystallographic characterization of a variety of new polyinterhalides, in which chloride functions as the central ion as shown by the molecular structures of [AsPh4 ][Cl(BrCl)3 ] and [CCl(NMe2 )2 ][Cl(BrCl)5 ]. Furthermore, the solid-state structure of an octahedrally coordinated nonclassical interhalide is reported for the first time. The tridecainterhalide monoanion [Cl(BrCl)6 ]- consists of a central chloride ion, which is coordinated by six BrCl molecules in a slightly distorted octahedral structure. All new compounds were characterized by single-crystal X-ray diffraction (XRD), NMR and Raman spectroscopy, as well as quantum-chemical calculations.
For decades the chemistry of polyhalides was dominated by polyiodides and more recently also by an increasing number of polybromides. However, apart from a few structures containing trichloride anions and a single report on an octachloride dianion, [Cl8 ]2- , polychlorine compounds such as polychloride anions are unknown. Herein, we report on the synthesis and investigation of large polychloride monoanions such as [Cl11 ]- found in [AsPh4 ][Cl11 ], [PPh4 ][Cl11 ], and [PNP][Cl11 ]â Cl2 , and [Cl13 ]- obtained in [PNP][Cl13 ]. The polychloride dianion [Cl12 ]2- has been obtained in [NMe3 Ph]2 [Cl12 ]. The novel compounds have been thoroughly characterized by NMR spectroscopy, single-crystal Raman spectroscopy, and single-crystal X-ray diffraction. The assignment of their spectra is supported by molecular and periodic solid-state quantum-chemical calculations.
The formation and experimental characterization of the first hexabromide dianion is presented. This dianion fills the last remaining gap in the series of polybromides from the tribromide [Br3 ]- to the undecabromide [Br11 ]- . The experimental results are compared to quantum-chemical calculations. These calculations predict-based on electrostatic interactions-a T-structure for the hexabromide dianion, while halogen-halogen bonding favors the hockey-stick-like structure experimentally found in the crystal structure. The hexabromide is built of two tribromide moieties, one of which is highly asymmetric. The classification of this unique anion as hexabromide dianion is discussed. The counter ion [C5 H10 N2 Br]+ stabilizes the hexabromide dianion by additional σ-hole interactions. The compound is fully characterized by mass spectrometry, NMR-, IR and single crystal Raman spectroscopies as well as single-crystal X-ray diffraction.
A systematic investigation on the existence of chloroiodates formed by reaction of Cl- with I2 Cl6 , apart from the well-known [ICl4 ]- , namely [I2 Cl7 ]- and [I3 Cl10 ]- , was undertaken by employing theoretical as well as experimental methods. The thermodynamic stability in terms of the complexation enthalpies and Gibbs energies, and also the decomposition of the iodine(III) polyinterhalogen anions through dichlorine elimination to form iodine (I) compounds, was studied by means of DFT and ab initio quantum-chemical calculations up to an extrapolated CCSD(T)/A'QZ level. On the experimental side, mixtures of [HMIM]Cl ([HMIM]+ =1-hexyl-3-methylimidazolium), [BMP]Cl ([BMP]+ =1-butyl-1-methylpyrrolidinium chloride) and [NEt4 ]Cl with 0.5, 1.0, and 1.5â equivalents of I2 Cl6 were investigated by single-crystal XRD, ion chromatography, NMR- and Raman spectroscopy. The reactions with 0.5â equivalents of I2 Cl6 resulted in the compounds [HMIM][ICl4 ], [BMP][ICl4 ], and [NEt4 ][ICl4 ], of which crystal structures were determined. The mixtures with 1.0 or 1.5â equivalents of I2 Cl6 yielded dark red liquids or suspensions of a dark red liquid with an orange solid, respectively. Both mixtures were studied by NMR-spectroscopy for the organic cation part and ion chromatography and Raman spectroscopy for the polyinterhalogen anions. The discussion of the experimental Raman spectra is supplemented with computed spectra based on the structures obtained from RI-MP2/def2-TZVPP structure optimisations. Overall [I2 Cl7 ]- appears to be the predominating anionic species in mixtures with 1.0â equivalents I2 Cl6 , while mixtures with 1.5â equivalents of I2 Cl6 are suspensions of I2 Cl6 in a liquid phase containing mixed anionic interhalogen complexes.
