8 Halogens and noble gases

A. K. Brisdon

Department of Chemistry, UMIST, Manchester, UK M60 1QD

1 Introduction

This chapter reviews the year 2001 literature for the elemental halogens and the noblegases and compounds containing these elements in their positive oxidation states. Asin previous years, publications which involve halide, interhalide or oxohalide anions ascounter ions are generally not described.

2 Halogens

Traditionally hydrogen bonding is considered to be the driving force for assembly oforganic molecules into extended structures. However, over recent years it has becomeobvious that other possibilities exist—one of which arises from the presence ofhalogen atoms in the compounds. The tendency of halogen atoms to interact withlone-pair possessing atoms has been referred to as halogen-bonding, the name beingdeliberately chosen to reflect the parallels between hydrogen- and halogen-bonding.This terminology has been used before, but it appears to have become more widelyaccepted and a number of reports and reviews in this area have now been published.Halogen-bonding may occur between two halogens, or between a halogen and a non-halogen. The former type of interaction is exemplified in a study of the structuresformed by a series of halogen- and methyl-substituted cis-9,10-diphenyl-9,10-dihydro-anthracene-9,10-diols. Whilst the solid-state structures of the methyl-substitutedcompounds are dictated by hydrogen bonds, for the halogen-substituted moleculesinterhalogen interactions compete with hydrogen bonding to direct the crystallinearrangement.1

Meanwhile, Metrangolo and Resnati have described the extensive self-assembly thatoccurs in the second type of interaction.2 Mixtures of iodofluorocarbons (asacceptors) and amines (as donors) generate N � � � I–Rf interactions that are specific,directional, and sufficiently strong to overcome the usual low affinity between per-fluorocarbon and hydrocarbon molecules, resulting in the self-assembly of a mixedsystem. DSC measurements were used to quantify the relative halogen-bonding andhydrogen-bonding interactions from which it was found that halogen-bonding is oftenat least 30% stronger. Understanding such halogen–halogen interactions shouldprovide a new tool which may be used to help drive structural and solvency effects.

DOI: 10.1039/b109581c Annu. Rep. Prog. Chem., Sect. A, 2002, 98, 107–114 107

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The generation of perfluorinated materials using dilute elemental fluorineis a well-established method which has been successfully applied to generatemany perfluorinated organic compounds and some of this area has been reviewed.3

A similar methodology has been shown to be viable in the preparation of per-fluorinated carborane nano-spheres from the analogous perprotio startingmaterial.4

The coordination of dihalogens to Lewis bases continues to attract researchers. Inthe past this has been a rich source of new structural motifs and those derived fromthe reactions between a range of sulfur and selenium donors with dihalogens andinterhalogens has been reviewed.5 Methods of tuning the interaction between selen-ium and iodine across the continuum from n σ* Se–I interactions, (3c, 4e) X–Se–Isystems, to van der Waals contacts have also been reviewed.6 Meanwhile, the nature ofone of these types of interactions, the hypervalent (3c, 4e) bond, has been investigatedin detail in a series of high level computational studies.7

More specifically, the interaction between N-methylbenzothiazole-2-selone withsulfuryl chloride in the solid state results in molecules of mbts�Cl2. In the solid statethese T-shaped molecules interact via Cl � � � Cl intermolecular contacts to generatean extended structure of interlocking molecules with a ‘zipper-like’ arrangement.8 Thereaction of dibromine with Ph3PNH results in a number of products, one of which isPh3PNBr�Br2,

9 the solid state molecular structure of which contains a moleculeof bromine coordinated to the nitrogen atom of a N-bromine–phosphoraneimine[d(Br–N) = 224.5 pm, d(Br–Br) = 248.8 pm]. The adducts formed between bis-(diphenylphosphino)methane disulfide or bis(diphenylphosphino)ethane disulfidewith iodine in dichloromethane solution results in dppmS�I4 and dppeS�I4, the bond-ing in which is consistent with S I2 interactions.10 The low-temperature single-crystalstructures of the products derived from the interaction of dibromine with benzeneand toluene reveal a localized form of bonding 11 rather than the coaxial structurereported previously. The dibromine molecule is orientated essentially perpendicular tothe aromatic ring and is located at the rim of the molecule as shown in Fig. 1. Byconsidering all the Br � � � C distances the interaction is interpreted as having ahapticity of 1.5, that is it lies half-way between over-atom (η1) and over-bond (η2)

Fig. 1 ORTEP representation of the dibromine adduct of benzene; thermal ellipsoids areshown at the 50% probability level.

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for C6H6�Br2, whilst in MeC6H5�Br2 preference is shown for an over-bond interaction(η = 1.7–1.86) centred on the ortho- and para-carbons.

Continued investigations of the gas-phase adducts of halogens with donors hasresulted in the publication of the ground-state rotational spectra of the complexesformed between water and dichlorine,12 difluorine or chlorine monofluoride withwater,13 and H2S with dibromine.14 Comparison of the data derived for theCl2 � � � H2O system with that previously reported for the HCl � � � H2O systemsupports the proposal that the halogen-bond can be considered as an analogue of thehydrogen-bond.

3 Interhalogens and polyhalide ions

Theoretical studies of the electron donor–acceptor complexes of the interhalogensIBr and ICl with bases such as diethyl ether, diethyl sulfide and trimethylamine con-firm that ICl is a stronger acceptor than IBr by virtue of the stronger electron-withdrawing effect of chlorine over bromine. However, whilst the computed groundstate structures of Et2O�IX and NH3�IX (X = Cl, Br) show axially coordinated inter-halogen molecules of C2v and C3v symmetry, respectively, for Et2S�IX the greatestoverlap is with the HOMO directed perpendicular to the Et–S–Et plane resulting inan adduct of Cs symmetry.15 Interhalogen adducts of a series of 1,2-bis(3-methyl-imidazolin-2-selone)ethanes have been reported resulting in the first T-shapedselenium adduct containing the I–Se–Br group.16 Reaction of 3,3-disubstitutedbornane-2-thiones with ICl or Br2, results in an unisolated intermediate thione–dihalogen complex which subsequently acts as an internal halogenating agent to givestereospecific monohalogenation of the starting material, Scheme 1.17

There have been a number of reports of new polyhalide ions. Previously Cl2F�,

ClF2� and ClF4

� (derived by fluoride abstraction using a Lewis acid from ClF, ClF3

and ClF5, respectively) have been reported, although of these, X-ray crystal data wasonly available for salts of ClF2

�. Single crystals of ClF4�SbF6

� have now beenobtained and they show a pseudo-trigonal bipyramidal geometry for the cation withtwo longer, more ionic, axial bonds and two shorter equatorial bonds, Fig. 2.18 Apseudo-octahedral arrangement around the central chlorine atom results frominteractions between the chlorine and neighbouring fluorides of two adjacent SbF6

�

anions to produce an infinite zigzag chain of alternating ClF4� and SbF6

� moieties.Generation of ClF6

� via fluoride abstraction is not possible, since the parentmolecule ClF7, and the bromine analogue do not exist. Alternative routes to ClF6

�

from ClF5 are limited due to the extreme oxidising power of the parent molecule. Ithas now been shown that both ClF6

� and BrF6� containing salts may be obtained by

Scheme 1

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reacting the appropriate pentafluoride with NiF4, which is in turn derived fromCs2NiF6 in the presence of arsenic pentafluoride.19 It is proposed that the powerfuloxidising agent NiF3

�AsF6� is generated in situ, which acts as a one-electron oxidiser

to give the ClF5� radical cation, Scheme 2. This subsequently reacts with either NiF3

or NiF4 to generate the hexafluorochlorate() salt.

This NiF4 based system, which appears to generate one of the most powerful oxidis-ing species available from commercial starting materials, offers a number of advan-tages over the alternatives, such as KrF� which are more difficult to handle, and it willbe interesting to see what other new high-oxidation state species are generated withthis system.

Although there are many known polyhalides of iodine the range of polybromides ismuch more limited, attempts to prepare Br7

� from [PPh4]�Br� with IBr resulted in the

first seven-membered polybromide I3Br4�.20 Crystals of the tetraphenylphosphonium

salt were obtained and show a distorted C3v symmetry in the anion which is bestdescribed as a bromide coordinated to three IBr units via the iodine atoms. The crystalstructure of [PPh4][ICl2] has also been reported and shows an anion that is symmetricand nearly linear [Cl–I–Cl = 178.10(6)�].21

The use of iodine interhalogens is well established in organic synthesis and con-tinues to show a number of interesting, and often, specific reactivities. For example,iodine monochloride, in the presence of aluminium trichloride, has been shown toeffect iodo-carbocyclization of α-iodo cycloalkanones.22 ICl in aqueous sulfuric acid

Fig. 2 ORTEP representation of the solid state structure of [ClF4]�[SbF6]

�, thermal ellipsoidsare drawn at the 50% probability level.

Scheme 2

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acts as a good iodinating agent for compounds such as biphenyl, fluorene and1-nitronapthalene, whilst chlorinated products are obtained for anthracene and phen-anthrene.23 The use of iodine pentafluoride in Et3N�HF is reported to give a stable,non-hazardous, easy to handle reagent for selective fluorination of organic substratesunder mild conditions.24 Finally, a study of applications of the much more reactivebromine trifluoride in organic chemistry has shown that a wide range of fluorinationreactions are possible in addition to its more traditional use as an oxidising agent.25

4 Halogen oxides and organoiodine compounds

Oxide fluorides of iodine are some of the most stable high oxidation state iodine-containing compounds, despite this the structure of IO2F, a compound which was firstreported in 1953, has remained unknown. This omission is even more obvious whencompared with the other iodine() oxides, fluorides and oxide fluorides (I2O5, IOF3

and IF5) all of which have known structures. Minkwitz and co-workers have nowobtained data for this compound which, in isolation, exhibits a pyramidal structure.26

However, when interactions to neighbouring molecules are considered, an alternativedescription appears more appropriate, see Fig. 3. An alternating axial–equatorial linked

trigonal-bipyramidal arrangement is apparent. The equatorial plane contains the twoI��O bonds [180.5(6) and 177.3(6) ppm] with the apical positions being occupied byone fluorine and one oxygen substituent [d(I–F) = 190.3(5) pm, d(I–O) = 222.6(6) pm].This is consistent with the previously reported vibrational spectroscopic data.

Compounds containing iodine in two different oxidation states are rare, com-proportionation often occurring to give the more stable oxidation state compound.However, an accidental discovery led to Cl2IOI(O)F2, the first example of aniodine oxofluoride chloride with mixed valency iodine atoms.27 The structure of this

Fig. 3 ORTEP representation of the solid state structure of IO2F, showing the interactionsbetween adjacent molecules, thermal ellipsoids are drawn at the 50% probability level. (Repro-duced by permission from Inorg. Chem., 2001, 40, 6494, Copyright 2001, American ChemicalSociety.)

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serendipitous compound is of two linked trigonal bipyramidal iodine centres, oneformally � the other �, linked by an oxygen bridge. A distorted bipyramidalstructure has also been reported for CF3IClF, the only known example of a ternaryinterhalogen compound containing a CF3 group, and formally a derivative of theunknown interhalogen IF2Cl.28

Hypervalent iodine compounds continue to find a number of applications inorganic synthesis. The reaction of diiodine with ArH in the presence of CrO3, as anoxidant, and HCl, results in a convenient one-pot synthetic method for the generationof ArICl2 molecules. The products, in turn, may be used as selective chlorinating oroxidising agents.29 The phenyliodine() bis(trifluoroacetate) reagent has been used togenerate high yields of p-quinones in aqueous solutions.30

Finally, oxidation of N-(2-iodobenzoyl) amino acids with dimethyl dioxirane hasafforded a trimeric benziodazole macrocycle containing hypervalent iodine centreswhich exhibit secondary I � � � O interactions. It is these interactions which arebelieved to result in the self-assembly that gives rise to the novel hypervalent iodinemacrocycle.31

5 Noble gases and noble gas compounds

The use of xenon as an NMR probe continues to be examined, with a number of newor improved applications. These include: xenon as a mechanistic probe of radicalintermediates in enzymic reactions,32 detection of conformational changes in sugar–protein binding using 129Xe NMR spectroscopy 33 and 131Xe NMR spectroscopy as aprobe of voids in solids.34

Following the initial discovery of the reactivity of the noble gases in the early1960s a number of compounds of the more electronegative elements (fluorine andoxygen) were prepared. Towards the end of the 20th century the rate at which newnoble-gas compounds were being reported slowed down, however, recently therehave been a number of new and exciting discoveries in this area, and this year hasseen a consolidation of these areas. Consistent with this is the appearance ofreviews of noble gas chemistry in general,35 and specifically dealing with the recentadvances in the formation and reactions of compounds containing xenon–carbonbonds.36

The reports last year of compounds of the lighter noble gases obtained byphotolysis of HF in a low-temperature argon matrix has resulted in intense interest inthese species. Further investigations by the research group that originally made thesediscoveries show that on annealing the matrix by raising the temperature to ca. 27 K amore stable configuration of HArF is obtained which exhibits ν(Ar–H) some 50 cm�1

higher than that previously reported.37 Theoretical studies have been undertaken andthese suggest that HArF adopts a strongly ionic equilibrium structure as illustrated inFig. 4, below.38

Fig. 4 The calculated bond lengths and (in parenthesis) Mulliken electron densities for HArF.

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Similar conclusions have been drawn by others undertaking theoretical studiesof HArCl,39 and for a series of compounds of the type HNgCN, HNgNC, HNgOH(Ng = Kr, Xe).40

Similarly, last years reports of the first metal–noble gas compound of appreciablestability has prompted others to undertake computational studies of this and relatedsystems. On the basis of this work it is suggested that various trivalent, tetravalent andeven hexavalent transition metal complexes of xenon and krypton may be intrinsicallystable.41

On studying the reaction between SbCl5 and [XeF]�[SbF6]� in HF–SbF5 solution a

number of products were obtained en route to an orange compound which was stableto �20 �C.42 This material was identified spectroscopically and by crystallography as[XeCl]�[Sb2F11]

�, shown in Fig. 5. The average Xe–Cl distance [230.7(2) pm] is shorter

than that recorded for any other xenon–chlorine contact, it corresponds with thepredictions for a Xe–Cl single bond and is comparable with that observed in theisoelectronic compound ICl.

A re-determination of the single X-ray crystal structures of KrF2 and the relatedspecies [KrF][MF6] and [Kr2F3][MF6] has confirmed that dimorphism occurs forKrF2

43 whilst computational studies of the gas-phase structure of XeF6 confirms alow energy barrier between the different possible structures, resulting in a non-staticstructure. A C3v symmetry molecule is predicted to possess the lowest energy and thesmall differences in energy between the different structures is interpreted using thePearson hardness model.44

Finally, it has been shown that 18F labelled XeF2 may be prepared by 18F fluorideexchange with XeF2, and that this may in-turn be used to prepare 18F labelledcompounds for positron emission tomography (PET) studies.45 The use of XeF2, incombination with trimethylsilylisocyanate in triflic acid has been shown to give a newsystem for the amination of aromatic compounds.46

Ligand/reagent abbreviations used in this chapter

Rf perfluoroalkyl or perfluoroaryl residue.DSC differential scanning calorimetrymbts N-methylbenzothiazole-2-selonedppmS bis(diphenylphosphino)methane disulfidedppeS bis(diphenylphosphino)ethane disulfide

Fig. 5 ORTEP representation of the solid state structure of [XeCl]�[Sb2F11]�; thermal ellipsoids

are drawn at the 50% probability level.

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References

1 I. Csoregh, T. Brehmer, P. Bombicz and E. Weber, Cryst. Eng., 2001, 4, 343.2 P. Metrangolo and G. Resnati, Chem. Eur. J., 2001, 7, 2511.3 J. S. Moilliet, J. Fluorine Chem., 2001, 109, 13.4 A. Herzog, R. P. Callahan, C. L. B. Macdonald, V. M. Lynch, M. F. Hawthorne and R. J. Lagow,

Angew. Chem., Int. Ed., 2001, 40, 2121.5 P. D. Boyle and S. M. Godfrey, Coord. Chem. Rev., 2001, 223, 265.6 W. W. DuMont, A. Martens-von Salzen, F. Ruthe, E. Seppala, G. Mugesh, F. A. Devillanova, V. Lippolis

and N. Kuhn, J. Organomet. Chem., 2001, 623, 14.7 J. Molina Molina and J. A. Dobado, Theor. Chem. Acc., 2001, 105, 328.8 P. D. Boyle, S. E. Davidson, S. M. Godfrey and R. G. Pritchard, Inorg. Chim. Acta., 2001, 325, 211.9 F. Kunkel, C. Maichle-Mössmer, J. Strähle and K. Dehnicke, Z. Anorg. Allg. Chem., 2001, 627, 2445.

10 D. C. Apperley, N. Bricklebank, M. B. Hursthouse, M. E. Light and S. J. Coles, Polyhedron, 2001, 20, 1907.11 V. A. Vasilyev, S. V. Lindeman and J. K. Kochi, Chem. Commun., 2001, 909.12 J. B. Davey, A. C. Legon and J. M. A. Thumwood, J. Chem. Phys., 2001, 114, 6190.13 S. A. Cooke, G. Cotti, C. M. Evans, J. H. Holloway, Z. Kisiel, A. C. Legon and J. M. A. Thumwood,

Chem. Eur. J., 2001, 7, 2295.14 A. C. Legon, Phys. Chem. Chem. Phys., 2001, 3, 2758.15 S. P. Anathaval and M. Manoharan, Chem. Phys., 2001, 269, 49.16 M. C. Aragoni, M. Arca, A. J. Blake, F. A. Devillanova, W. W. DuMont, A. Goran, F. Isaia, V. Lippolis,

G. Verani and C. Wilson, Angew. Chem., Int. Ed., 2001, 40, 4229.17 K. Shimada, T. Nanae, S. Aoyagi, Y. Takikawa and C. Kabuto, Tetrahedron Lett., 2001, 42, 6167.18 K. O. Christe, X. Zhang, J. A. Sheehy and R. Bau, J. Am. Chem. Soc., 2001, 123, 6338.19 T. Schroer and K. O. Christe, Inorg. Chem., 2001, 40, 2415.20 R. Minkwitz, M. Berkei and R. Ludwig, Inorg. Chem., 2001, 40, 25.21 R. Minkwitz and M. Berkei, Z. Naturforsch., Teil B., 2001, 56, 39.22 C. K. Sha, F. C. Lee and H. H. Lin, Chem. Commun., 2001, 39.23 V. K. Chaikovskii and V. D. Filimonov, Russ. J. Org. Chem., 2001, 37, 1130.24 N. Yoneda and T. Fukuhara, Chem. Lett., 2001, 222.25 S. Rozen and I. Ben-David, J. Org. Chem., 2001, 66, 496.26 R. Minkwitz, M. Berkei and R. Ludwig, Inorg. Chem., 2001, 40, 6493.27 R. Minkwitz and M. Berkei, Eur. J. Inorg. Chem., 2001, 457.28 R. Minkwitz and M. Berkei, Inorg. Chem., 2001, 40, 36.29 M. A. Anderson, Y. Xu and C. B. Grissom, J. Am. Chem. Soc., 2001, 123, 6720.30 N. Obeid and L. Skulski, Molecules, 2001, 6, 869.31 H. Tohma, H. Morioka, Y. Harayama, M. Hashizume and Y. Kita, Tetrahedron Lett., 2001, 42, 6899.32 V. V. Zhdankin, A. E. Koposov, J. T. Smart, R. R. Tykwinski, R. McDonald and A. Morales-Izquierdo,

J. Am. Chem. Soc., 2001, 123, 4095.33 S. M. Rubin, M. M. Spence, I. E. Dimitrov, E. J. Ruiz, A. Pines and D. E. Wemmer, J. Am. Chem. Soc.,

2001, 123, 8616.34 I. L. Mondrakovski, C. I. Ratcliffe and J. A. Ripmeester, J. Am. Chem. Soc., 2001, 123, 2066.35 K. O. Christe, Angew. Chem., Int. Ed., 2001, 40, 1419.36 H. J. Frohn and V. V. Bardin, Organometallics, 2001, 20, 4750.37 L. Khriachtchev, M. Pettersson, A. Lignell and M. Räsänen, J. Am. Chem. Soc., 2001, 123, 8760.38 N. Runeberg, M. Pettersson, L. Khriachtchev, J. Lundell and M. Räsänen, J. Chem. Phys., 2001, 114, 836.39 S. A. C. McDowell, J. Phys. Chem., 2001, 114, 8395.40 S. Berski, Z. Latajka, B. Silvi and J. Lundell, J. Chem. Phys., 2001, 114, 4349.41 W. P. Hu and C.-H. Huang, J. Am. Chem. Soc., 2001, 123, 2340.42 S. Siedel and K. Seppelt, Angew. Chem., Int. Ed., 2001, 40, 4225.43 J. F. Lehmann, D. A. Dixon and G. J. Schrobilgen., Inorg. Chem., 2001, 40, 3002.44 D. Yu and Z. Chen, THEOCHEM, 2001, 540, 29.45 M. Constantinou, F. I. Aigbirhio, R. G. Smith, C. A. Ramsden and V. W. Pike, J. Am. Chem. Soc., 2001,

123, 1780.46 N. Sh. Pirkaliev, V. K. Brel, N. G. Akhmedov, N. S. Zefirov and P. J. Stang, Medeleev Commun., 2001, 11,

172.

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