Oxohalide

Source: Wikipedia, the free encyclopedia.

In

crystalline substances with the same overall chemical formula, but having an ionic
structure.

Synthesis

Chromyl chloride liquid and vapour

Oxohalides can be seen as compounds intermediate between oxides and halides. There are three general methods of synthesis:[1]

  • Partial oxidation of a halide:
    2 PCl3 + O2 → 2 POCl3
    • In this example, the oxidation state increases by two and the electrical charge is unchanged.
  • Partial halogenation of an oxide:
    2 V2O5 + 6 Cl2 + 3 C → 4 VOCl3 + 3 CO2
  • Oxide replacement:
    CrO2−4 + 2 Cl− + 4 H+ → CrO2Cl2 + 4 H2O

In addition, various oxohalides can be made by halogen exchange reactions and this reaction can also lead to the formation of mixed oxohalides such as POFCl2 and CrO2FCl.

Properties

In relation to the oxide or halide, for a given oxidation state of an element A, if two halogen atoms replace one oxygen atom, or vice versa, the overall charge on the molecule is unchanged and the

covalent compounds of phosphorus in the +5 oxidation state. If an oxygen atom is simply replaced by a halogen atom the charge increases by +1, but the coordination number is unchanged. This is illustrated by the reaction of a mixture of a chromate or dichromate salt and potassium chloride with concentrated sulfuric acid
.

Cr2O2−7 + 4 Cl− + 6 H+ → 2 CrO2Cl2 + 3 H2O

The chromyl chloride produced has no electrical charge and is a volatile covalent molecule that can be distilled out of the reaction mixture.[2]

Oxohalides of elements in high oxidation states are strong oxidizing agents, with oxidizing power similar to the corresponding oxide or halide. Most oxohalides are easily hydrolyzed. For example, chromyl chloride is hydrolyzed to chromate in the reverse of the synthetic reaction, above. The driving force for this reaction is the formation of A-O bonds which are stronger than A-Cl bonds. This gives a favourable enthalpy contribution to the Gibbs free energy change for the reaction[3]

Many oxohalides can act as

trigonal bipyramidal complex VOCl2(N(CH3)3)2 with the base trimethylamine.[4]

The

vibrational spectra of many oxohalides have been assigned in detail. They give useful information on relative bond strengths. For example, in CrO2F2, the Cr–O stretching vibrations are at 1006 cm−1 and 1016 cm−1 and the Cr–F stretching vibrations are at 727 cm−1 and 789 cm−1. The difference is much too large to be due to the different masses of O and F atoms. Rather, it shows that the Cr–O bond is much stronger than the Cr–F bond. M–O bonds are generally considered to be double bonds and this is backed up by measurements of M–O bond lengths. It implies that the elements A and O are chemically bound together by a σ bond and a π bond.[5]

Oxohalides of elements in high oxidation states are intensely coloured owing to ligand to metal charge transfer (LMCT) transitions.[6]

Boron teflate.
  Boron
  Oxygen
  Tellurium
  Fluorine

Main group elements

Sulfuryl fluoride
F5AOAF5 (A = S, Se, Te)

Carbon group

Carbon

carbonyl compounds.[7]
For example:

COCl2 + 2 ROH → CO(OR)2 + 2 HCl

Silicon tetrafluoride reacts with water to yield poorly-characterized oxyfluoride polymers, but slow and careful reaction at -196 °C yields the oxyfluoride hexafluorodisiloxane as well.[8]

Pnictogens

isoelectronic with the nitrate
ion, NO−3. Only oxohalides of phosphorus(V) are known.[9]

Chalcogens

Sulfur forms oxohalides[10] in oxidation state +4, such as thionyl chloride, SOCl2 and oxidation state +6, such as sulfuryl fluoride (SO2F2), sulfuryl chloride (SO2Cl2), and thionyl tetrafluoride (SOF4). All are easily hydrolyzed. Indeed, thionyl chloride can be used as a dehydration agent as the water molecules are converted into gaseous products, leaving behind the anhydrous solid chloride.[11]

MgCl2·6H2O + 6 SOCl2 → MgCl2 + 6 SO2 + 12 HCl

Selenium and tellurium form similar compounds and also the oxo-bridged species F5AOAF5 (A = S, Se, Te). They are non-linear with the A-O-A angle of 142.5, 142.4 and 145.5° for S, Se and Te, respectively.[12] The tellurium anion F5TeO−, known as teflate, is a large and rather stable anion, useful for forming stable salts with large cations.[11]

Halogens

The halogens form various oxofluorides with formulae XO2F (chloryl fluoride), XO3F (perchloryl fluoride) and XOF3 with X = Cl, Br and I. IO2F3 and IOF5 are also known.[13]

Noble gases

Xenon forms xenon oxytetrafluoride (XeOF4), xenon dioxydifluoride (XeO2F2) and xenon oxydifluoride (XeOF2).

Transition metals and actinides

Crystal structure of Ti(ClO4)4.[14]
  Titanium
  Chlorine
  Oxygen

A selection of known oxohalides of transition metals is shown below, and more detailed lists are available in the literature.[15] X indicates various halides, most often F and Cl.

Oxidation state oxohalides
3 VOCl, VOBr,
FeOCl
4 [TiOCl4]2−, Cl3TiOTiCl3, VOCl2, [VOCl4]2−
5 VOX3, VO2F, [CrOF4]−, [CrOF5]2−, MnOCl3, TcOCl3, VOF3, VOCl3, NbOCl3
6
WOF4, WOCl4
7 MnO3F, ReOF5, ReO2F3, ReO3F, ReO3Cl,ReO3Cl, OsOF5
8 OsO2F4, OsO3F2
Structure of [Ta2OCl10]2−. Ru, Os form similar complexes.
[AgOTeF5-(C6H5CH3)2]2 molecule.[17] (Hydrogen atoms not shown.)
  Carbon (C)
  Fluorine (F)
  Oxygen (O)
  Tellurium (Te)
  Silver (Ag)

High oxidation states of the metal are dictated by the fact that

octahedral.[18]
The d1 complex ReOCl4 is square pyramidal.


The compounds [Ta2OX10]2− and [M2OCl10]4− (M = W, Ru, Os) have two MX5 groups joined by a bridging oxygen atom.[19] Each metal has an octahedral environment. The unusual linear M−O−M structure can be rationalized in terms of molecular orbital theory, indicating the presence of dπ — pπ bonding between the metal and oxygen atoms.[20] Oxygen bridges are present in more complex configurations like M(cp)2(OTeF5)2 (M = Ti, Zr, Hf, Mo or W; cp = cyclopentadienyl, η5-C5H5)[21] or [AgOTeF5-(C6H5CH3)2]2.[17]

In the actinide series, uranyl compounds such as uranyl chloride (UO2Cl2) and [UO2Cl4]2− are well known and contain the linear UO2 moiety. Similar species exist for neptunium and plutonium.

Minerals and ionic compounds

Crystal structure of bismoclite. Colours: red – O, green – Cl, grey – Bi.

Mohs 2–2.5) and most other oxohalide minerals.[22] Those other minerals include terlinguaite Hg2OCl, formed by the weathering of mercury-containing minerals.[23] Mendipite, Pb3O2Cl2, formed from an original deposit of lead sulfide
in a number of stages is another example of a secondary oxohalide mineral.

The elements iron, antimony, bismuth and lanthanum form oxochlorides of general formula MOCl. MOBr and MOI are also known for Sb and Bi. Many of their crystal structures have been determined.[24]

See also

References

  1. ^ Synthesis of individual compounds can be found in Housecroft & Sharpe and Greenwood & Earnshaw in sections relating to the specific element, A
  2. ^ Sisler, H. H. "Chromyl Chloride" Inorganic Synthesis McGraw-Hill: New York, 1946; Vol. 2, pp. 205–207.
  3. ^ Greenwood & Earnshaw, p. 1023
  4. ^ Greenwood & Earnshaw, p. 996.
  5. ISBN 0-471-19406-9
    , Tables II-4c, II-6g, II-6h, II-7b, II-8c
  6. ^ Shriver & Atkins, Figure 13.8, p. 447
  7. ^ Shriver & Atkins, p. 358
  8. doi:10.1021/ja00709a015
    .
  9. ^ Housecroft & Sharpe, pp. 329–330
  10. ^ Housecroft & Sharpe, pp. 365–367
  11. ^ a b Shriver & Atkins, p. 397
  12. doi:10.1002/anie.197800691
    .
  13. ^ Housecroft & Sharpe, p. 395
  14. doi:10.1021/ic00229a019
    .
  15. ^ Greenwood & Earnshaw, Chapters 22–25, section halides and oxohalides
  16. ^ Greenwood & Earnshaw p. 993.
  17. ^
    doi:10.1021/ic00219a022
    .
  18. ^ Housectroft & Sharpe, Chapters 21 and 22 illustrate many structures, including M-O and M-Cl bond lengths.
  19. doi:10.1039/DT9770000978.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )    . The structure is illustrated in Housectroft & Sharpe, Figure 22.5.
  20. ^ Housectroft & Sharpe, Figure 22.15.
  21. doi:10.1039/DT9960000509
    .
  22. ISBN 0-9622097-2-4
    . Retrieved December 5, 2011.
  23. doi:10.2475/ajs.s4-24.141.259
    . Retrieved 2009-05-21.
  24. ^ Wells, pp. 390–392

Bibliography

Wikimedia Commons has media related to Oxohalides.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Oxohalide&oldid=1164889352"