Cluster halogenation of adamantane and its derivatives with bromine and iodine monochloride

Noncatalytic halogenation of adamantane with Br2 or ICl proceeds according to the cluster mechanism featuring high kinetic order in halogen and a sharp decrease in DFT energy barrier when additional halogen molecules are involved in the system.

In Situ Synthesis and Applications for Polyinterhalides Based on BrCl

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.

Opening the Third Century of Polyhalide Chemistry: Thermally Stable Complex with "Trapped" Dichlorine

Unlike polyhalides of heavier halogens, polychlorides still remain exotic curiosities. Herein, we report preparation and investigation of complexes Cat₂ {[TeCl₆ ](Cl₂ )} (cat=1-methylpyridinium (1) and tetramethylammonium (2)) where dichlorine units are "trapped" by chlorotellurate(IV) anions via a system of non-covalent Cl⋅⋅⋅Cl interactions. Complex 2 reveals a record thermal stability (>100 °C) for inclusion compounds with Cl₂ , indications that such compounds can be used as solid Cl₂ source.

Synthesis and Characterization of [Br3 ][MF6 ] (M=Sb, Ir), as well as Quantum Chemical Study of [Br3 ]+ Structure, Chemical Bonding, and Relativistic Effects Compared with [XBr2 ]+ (X=Br, I, At, Ts) and [TsZ2 ]+ (Z=F, Cl, Br, I, At, Ts)

[Br₃ ][SbF₆ ] and [Br₃ ][IrF₆ ] were synthesized by interaction of BrF₃ with Sb₂ O₃ or iridium metal, respectively. The former compound crystallizes in the orthorhombic space group Pbcn (No. 60) with a=11.9269(7), b=11.5370(7), c=12.0640(6) Å, V=1660.01(16) ų , Z=8 at 100 K. The latter compound crystallizes in the triclinic space group P 1 ‾ (No. 2) with a=5.4686(5), b=7.6861(8), c=9.9830(9) Å, α=85.320(8), β=82.060(7), γ=78.466(7)°, V=406.56(7) ų , Z=2 at 100 K. Both compounds contain the cation [Br₃ ]⁺ , which has a bent structure and is coordinated by octahedron-like anions [MF₆ ]^- (M=Sb, Ir). Experimentally obtained cell parameters, bond lengths, and angles are confirmed by solid-state DFT calculations, which differ from the experimental values by less than 2 %. Relativistic effects on the structure of the tribromonium(1+) cation are studied computationally and found to be small. For the heaviest analogues containing At and Ts, however, pronounced relativistic effects are found, which lead to a linear structure of the polyhalogen cation.

Halogen bonding-assisted assembly of bromoantimonate(v) and polybromide-bromoantimonate-based frameworks

Halogen bonding within bromo- and polybromoantimonates(v).

Probing the speciation of quaternary ammonium polybromides by voltammetric tribromide titration

The speciation of quaternary ammonium polybromides (QBr_2n+1) was quantitatively determined by voltammetric tribromide titration on a Pt ultramicroelectrode (UME).

Synthesis and crystal structures of non-symmetric 1,3-di(alkyloxy)imidazolium salts

A series of non-symmetric 1,3-di(alkyloxy)imidazolium salts were synthesized by stepwise alkylation of 1-hydroxyimidazole-3-oxide. The quaternary salts were subsequently functionalized by bromination in 2-position. A 2-azidoimidazolium salt and an imidazoline-2-thione were prepared exemplarily. Crystal structures of two 2-bromo-1-alkyloxy-3-methyloxyimidazolium tribromides and a mercury(II)-thione complex have been determined by X-ray diffraction.

Factors influencing the formation of polybromide monoanions in solutions of ionic liquid bromide salts

Six different bromide salts - tetraethylammonium bromide ([N2,2,2,2]Br, Br), 1-ethyl-1-methylpiperidinium bromide ([C2MPip]Br, Br), 1-ethyl-1-methylpyrrolidinium bromide ([C2MPyrr]Br, Br), 1-ethyl-3-methylimidazolium bromide ([C2MIm]Br, Br), 1-ethylpyridinium bromide ([C2Py]Br, Br), and 1-(2-hydroxyethyl)pyridinium bromide ([C2OHPy]Br, Br) - were studied in regards to their capacity to form polybromide monoanion products on addition of molecular bromine in acetonitrile solutions. Using complementary spectroscopic and computational methods for the examination of tribromide and pentabromide anion formation, key factors influencing polybromide sequestration were identified. Here, we present criteria for the targeted synthesis of highly efficient bromine sequestration agents.

Noncatalytic bromination of benzene: A combined computational and experimental study

The noncatalytic bromination of benzene is shown experimentally to require high 5-14 M concentrations of bromine to proceed at ambient temperatures to form predominantly bromobenzene, along with detectable (<2%) amounts of addition products such as tetra and hexabromocyclohexanes. The kinetic order in bromine at these high concentrations is 4.8 ± 0.06 at 298 K and 5.6 ± 0.11 at 273 K with a small measured inverse deuterium isotope effect using D6 -benzene of 0.97 ± 0.03 at 298 K. These results are rationalized using computed transition states models at the B3LYP+D3/6-311++G(2d,2p) level with an essential continuum solvent field for benzene applied. The model with the lowest predicted activation free energies agrees with the high experimental kinetic order in bromine and involves formation of an ionic, concerted, and asynchronous transition state with a Br8 cluster resembling the structure of the known Br9 (-). This cluster plays three roles; as a Br(+) donor, as a proton base, and as a stabilizing arm forming weak interactions with two adjacent benzene CH hydrogens, these aspects together combining to overcome the lack of reactivity of benzene induced by its aromaticity. The computed inverse kinetic isotope effect of 0.95 agrees with experiment, and arises because C-Br bond formation is essentially complete, whereas C-H cleavage has not yet commenced. The computed free energy barriers for the reaction with 4Br2 and 5Br2 for a standard state of 14.3 M in bromine are reasonable for an ambient temperature reaction, unlike previously reported theoretical models involving only one or two bromines.

The formation of high-order polybromides in a room-temperature ionic liquid: from monoanions ([Br5 ](-) to [Br11 ](-) ) to the isolation of [PC16 H36 ]2 [Br24 ] as determined by van der Waals Bonding Radii

An unprecedented diversity of high-order bromine catenates (anionic polybromides) was generated in a tetraalkylphosphonium-based room temperature ionic liquid system. Raman spectroscopy was used to identify polybromide monoanions ranging from [Br5 ](-) to [Br11 ](-) in the bulk solution, while single-crystal X-ray diffraction identified extended networks of linked [Br11 ](-) units, forming a previously unknown polymeric [Br24 ](2-) dianion. This represents the largest polybromide species identified to date. In combination with recent work, this suggests that other, higher order molecular polybromide ions might be isolated.

Structures, vibrational frequencies, and stabilities of halogen cluster anions and cations, X(n)(+/-), n = 3, 4, and 5

The structures, vibrational frequencies, and thermodynamic stabilities of the homonuclear polyhalogen ions, X3(+), X3(-), X4(+), X4(-), X5(+), and X5(-) (X = Cl, Br, I), have been calculated at the CCSD(T) level. The energetics were calculated using the Feller-Peterson-Dixon approach for the prediction of reliable enthalpies of formation. The calculations allow the following predictions where stabilities are defined in terms of thermodynamic quantities. (1) The X3(+) cations are stable toward loss of X2; (2) the X3(-) anions are marginally stable toward loss of X2 with Cl3(-) being the least stable; (3) the X4(+) cations and X4(-) anions are only weakly bound dimers of X2(+1/2) and X2(-1/2) units, respectively, but the cations are marginally stable toward decomposition to X3(+) and X, with I4(+) having the lowest dissociation energy, whereas the X4(-) anions decompose spontaneously to X3(-) and X; (4) the X5(+) cations are only marginally stable at low temperatures toward loss of X2, with Cl5(+) being the least stable; and (5) the X5(-) anions are also only stable at low temperatures toward loss of X2, with Cl5(-) being the least stable.