Chlorine Oxide (V): Properties, Structure, Uses

The chlorine oxide (V) is a highly unstable inorganic compound whose chemical formula is Cl 2 O 5 . It is one of the many chlorine oxides, which are characterized by being molecular, or even radical species.

Cl 2 O 5 has only found life on paper and theoretical calculations; however, its existence has not been ruled out and it is probable that some can be characterized (by advanced spectroscopy techniques). What can be predicted from general chemistry concepts of this oxide is that it is the anhydride of chloric acid, HClO 3 .

Cl2O5 molecule. Source: Jynto [CC0].

The hypothetical chlorine (V) oxide molecule is shown above. Note that since it is a molecule, the presence of the Cl +5 ion is not considered at all ; even less so when it must have such a polarizing power to force oxygen to bind covalently.

Like any unstable compound, it releases energy to break down into more stable products; process that in many cases is explosive. When Cl 2 O 5 decomposes it releases ClO 2 and O 2 . It is theorized that in water, depending on the isomer of Cl 2 O 5 , various chlorine oxo acids can form.

Article index

  • one

    Properties (edit)

  • two

    Structure of chlorine oxide (V)

    • 2.1


    • 2.2

      Lewis structure

    • 23

      Isomers and their respective hydrolysis

  • 3


  • 4


  • 5


Properties (edit)

The molar mass of Cl 2 O 5 is 150.9030 g / mol. From this mass, and its hypothetical molecule, it can be conjectured that if it could be isolated, it would probably be an oily liquid; of course, comparing it with the physical appearance of Cl 2 O 7 .

Although it cannot be isolated or characterized, this chlorine oxide is acidic, covalent and must also have a small dipole moment. Its acidity is understandable if the chemical equation of its hydrolysis is analyzed:

Cl 2 O 5  + H 2 O 2HClO 3

The HClO 3 being chloric acid. The reverse reaction would result in the case that the acid can be dehydrated:

2HClO => Cl 2 O 5  + H 2 O

On the other hand, when Cl 2 O 5 is barely produced, it decomposes:

2Cl 2 O 5 => 4ClO 2 + O 2

It is therefore an intermediary species rather than an oxide properly speaking. Its decomposition must be so fast (considering that Cl 2 O 5 is even formed ), that it has not been detected by current instrumental analysis techniques.

Structure of chlorine oxide (V)


The upper image shows the structure of the hypothetical Cl 2 O 5 molecule with a spheres and rods model. The red spheres represent oxygen atoms, and the green spheres represent chlorine atoms. Each chlorine has a trigonal pyramid environment, so its hybridization must be sp 3 .

Thus, the Cl 2 O 5 molecule can be seen as two trigonal pyramids joined by an oxygen. But if you look carefully, one pyramid orients its oxygen atoms downward, the other out of plane (toward the reader).

Hence it is presumed that there are rotations in the O 2 Cl-O-ClO 2 bond , making the molecule relatively dynamic. Note that the formula O 2 ClOClO 2 is a way of representing the structure of Cl 2 O 5 .

Lewis structure

Lewis structure for the hypothetical Cl2O5. Source: Gabriel Bolívar.

Until now the molecule by itself has not made it possible to decipher what its instability is due to. To shed light on this question, we turn to its Lewis structure, depicted above. Note that the structure may be mistakenly thought to be flat, but in the previous subsection it was clarified that this is not the case.

Why do both chlorine atoms have positive formal charges? Because chlorine has a free pair of electrons left, which can be verified by applying the Valencia Bond Theory (which will not be done here for simplification purposes). Thus, its formal load is:

C f = 7 – (4 + 2) = 1

And what does this have to do with its instability? Well, chlorine is considerably electronegative, and therefore a poor carrier of positive formal charges. This makes Cl 2 O 5 a highly acidic species, since it needs to gain electrons to supply the electronic demand for the two chlorines.

The opposite happens with Br 2 O 5 and I 2 O 5 , oxides that do exist under normal conditions. This is because both bromine and iodine are less electronegative than chlorine; and therefore, they better support the positive formal charge.

Isomers and their respective hydrolysis

So far all the explanation has fallen on one of the two isomers of Cl 2 O 5 : O 2 ClOClO 2 . Which is the other? The O 3 ClOClO. In this isomer the chlorines lack formal positive charges, and should therefore be a more stable molecule. However, both O 2 ClOClO 2 and O 3 ClOClO should undergo hydrolysis reactions:

O 2 Cl-O-ClO 2 + H 2 O => 2O 2 Cl-OH (which are nothing more than HClO 3 )

O 3 Cl-O-ClO + H 2 O => O 3 Cl-OH (HClO 4 ) + HO-ClO (HClO 2 )

Note that up to three chlorine oxo acids can be formed: HClO 3 , HClO 4, and HClO 2


Its name ‘chlorine oxide (V)’ corresponds to the one assigned according to the stock nomenclature. Cl 2 O 5 can also have two other names: dichloro pentaoxide and chloric anhydride, assigned by the systematic and traditional nomenclatures, respectively.


Rather than motivating computational studies, Cl 2 O 5 will be of no use until it is discovered, isolated, characterized, stored and shown not to explode at the slightest contact.


  1. Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
  2. Sandra Luján Quiroga and Luis José Perissinotti. (2011). Chlorine Oxoacids and Structure of Dichlorine Oxides. Chem. Educator, Vol. 16 .
  3. Chemical formulation. (2019). Chlorine oxide (V). Recovered from:
  4. Linus Pauling. (1988). General Chemistry. Dover Publications, INC., New York.
  5. Richard C. Ropp. (2013). Encyclopedia of the Alkaline Earth Compounds. ElSevier.

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