What are two uses of interhalogen compounds

content1 Introduction 2. hydrogen3. Noble gases4. Halogens5. Chalcogens6. Pentele7. Tetrele8. Boron

Compounds of the halogens with one another (so-called interhalogen compounds) have the general formulas XY, XY3, XY5, XY7 known, where

  • X is always the more electropositive halogen, which is correspondingly present in the oxidation states +1, +3, +5 and +7.
  • Y is in most cases fluorine, and in rare cases also chlorine. Y is always in the -1 oxidation state.
The interhalogen compounds are reactive, typically covalent compounds, all of which are derived from the elements or by fluorination with XeF2 can be produced.
The overview in Figure 4.3.1. graphically shows the known interhalogen compounds as colored squares. Varies in this diagram
  • to the top the composition,
  • in front the ligand (i.e. the more electronegative partner Y)
  • and to the right the central atom (more electropositive partner X).
Fig. 4.3.1. Overview of interhalogen compounds‣SVG
This diagram shows general tendencies regarding existence, stability and reactivity and the fundamental difference between the simplest interhalogens XY and the higher compounds XYn (n> 1) becomes clear. For the simple interhalogen compounds XY, all combinations are known (base area of ​​the diagram in Fig. 4.3.1). The bond in these simple compounds corresponds to that of the halogens themselves, but it is polar and therefore the compounds are generally more reactive than the simple halogens. From the diagram in Fig. 4.3.1. the predictable tendencies and properties for these compounds follow:
  • In the ranks
    • IF, BrF, ClF, F2
    • ICl, BrCl, Cl2
    • IBr, Br2
    the boiling and melting points fall, the reactivity increases, the tendency to disproportionate decreases.
ClF is a colorless gas, BrF is a light red gas. IF, on the other hand, is a brown solid. IBr is also fixed, as shown in Figure 4.3.2. shows.
4.3.2. IBr
The further apart X and Y are in the periodic table, the more reactive are the simple interhalogens XY:
  • ClF is very stable.
  • BrF is not very stable and tends to disproportionate in Br2 and BrF3.
  • IF is only below -14 OC stable. Above this temperature it disproportionates in I.2 and IF5.
With water, the electronegative partners Y of the interhalogens are reduced to halide, the more electropositive partners X are oxidized to the hypohalites: In the case of the higher interhalogen compounds (XYn (n> 1) except for ICl3 around fluoride (back wall of the diagram in Fig. 4.3.1). All compounds are sensitive to hydrolysis and act as strong fluorinating and oxidizing agents. With increasing fluorine content they show increased volatility. Only iodine forms the heptafluoride. The structures can be explained with the help of the VSEPR concept (Gillespie-Nyholm concept). For the individual groups ... Among the compounds of general composition XY3 are all fluoride as well as ICl3 known. According to the VB method, binding can only be achieved if a sp3d-hybrids. These are T-shaped molecules (trigonal bipyramids, both lone pairs are equatorial). ICl is an exception3, which as a dimer (ICl3)2 is present.
4.3.2. Molecular structure of I2Cl6‣SVG and ‣VRMLFig. 4.3.3. ICl3
Due to their low self-dissociation, the substances have electrical conductivity:
2 BrF3 <---> BrF2+ + BrF4-
The compounds are amphoteric, i.e. they enter into Lewis acid-base reactions. The interhalogens (mostly BrF3) can therefore be used as reaction media:
  • Effect as a Lewis acid:
    KF + BrF3 ---> KBrF4 (---> K+ + BrF4-)
  • Effect as a Lewis base:
    BrF3 + SnF4 ---> (BrF2)2SnF6 (---> 2 BrF2+ + SnF62-)
  • Neutralization reactions:
    (BrF2) SbF6 + Ag (BrF4) ---> AgSbF6 + 2 BrF3
    according to the reaction of water:
    OH- + H+ ---> H2O
  • Redox reactions:
    • Reduction:
      2 BrF2+ + 2 e- ---> BrF3 + BrF
      according to the reaction of water:
      H+ + e- ---> 1/ 2 H2
    • Oxidation:
      2 BrF4- ---> BrF3 + BrF5 + 2 e-
      according to the reaction of water:
      2 OH- ---> 1/2O2 + H2O + 2 e-
BrF3 can therefore be used to dissolve noble metals and metal halides under oxidation after:
Ag ---> AgF ---> Ag+ + BrF4-
can be used. Chlorine trifluoride, ClF3, is one of the most reactive chemical substances and reacts explosively with almost all substances. All fluoride XF5 are known. They are less reactive than the corresponding XY3-Links. To describe the bond according to the valence bond method, a sp3d2-Hybrid can be assumed, the molecular structure can be described as ψ-octahedron. IF5 is a technical product that is used for the fluorination / iodination of organic compounds for polymer production. The only known compound of this type is IF7. According to the VB description, the chemical bond is via a sp3d3-Hybrid to describe. This also makes it clear that only the iodine compound is known here, since the promotion energy of electrons in d-states is lower in the heavier elements. In the gas, the F ligands are in IF7 fluctuating, in the solid the molecule forms a pentagonal bipyramid (see Fig. 4.3.4.).
Fig. 4.3.4. Molecular structure of IF7 in the solid‣VRML
In addition to the neutral interhalogen compounds, there are also due to the Lewis acid-base property
  • cationic complexes of type XY2+; XY4+, XY6+ such as [ICl2]+, [ClF4]+ or [IF6]+ and
  • anionic complexes of the type XY-, XY4- and XY6- such as [Br3]-, [ClF2]-, [BrF4]- or [BrF6]-
known. The structures can be explained like those of the neutral interhalogens according to the VSEPR concept:
  • cationic complexes:
    • XY2+ = 7 + 2 - 1 = 8 outer electrons = 4 pairs = tetrahedron
    • XY4+ = 7 + 4 - 1 = 10 outer electrons = 5 pairs = trigonal bipyramid
    • XY6+ = 7 + 6 - 1 = 12 outer electrons = 6 pairs = octahedron
  • anionic complexes:
    • XY2- = 7 + 2 + 1 = 10 outside-e- = 5 pairs = trigonal bipyramid
    • XY4- = 7 + 4 + 1 = 12 outside-e- = 6 pairs = octahedron = planar molecule
    • XY6- = 7 + 6 + 1 = 14 outside-e- = 7 pairs = NONE !!! disturbed octahedron
In the polyiodides and the polyiodine cations (see Fig. 4.3.5.), Iodine occurs both as a ligand and as a central atom, so that further linkage is also possible.
Fig. 4.3.5. Overview of poly-iodine anions and cations‣SVG
In detail are
  • Anions, mostly in salts with Cs+ or the like as counterions, e.g.
    • [I.3]- (arises from KI and I.2; isoelectronic to XeF2, 24 e--System)
    • [I.4]2- (I.2 with two condensed I.-)
    • [I.5]- (responsible for the blue coloration of iodic acid; I.- with two condensed I.2)
    • also I.82-, I.7-, I.9- to I.164- and
  • Cations, mostly with SbF6-Counterion, such as
    • [I.3]+ (angled, isoelectronic to SCl2, 22 e--System)
    • [I.4]2+, I.5+ .. to I153+
known. content1 Introduction 2. hydrogen3. Noble gases4. Halogens5. Chalcogens6. Pentele7. Tetrele8. Boron