Interhalogen Compounds

Interhalogen compounds are compounds formed when halogen group elements react with each other. There are four types of interhalogen compounds. They are as follows:

· XY

· XY₃ 

· XY₅ 

· XY₇ 

where X is halogen of larger size and X′ of smaller size and X is more electropositive than X′ . As the ratio between radii of X and X ′ increases, the number of atoms per molecule also increases. Thus, iodine (VII) fluoride should have maximum number of atoms as the ratio of radii between I and F should be maximum. That is why its formula is IF₇ (having maximum number of atoms).

Preparation

The interhalogen compounds can be prepared by the direct combination or by the action of halogen on lower interhalogen compounds. The product formed depends upon some specific conditions, For example,

Properties

Some properties of interhalogen compounds

Type	Formula	Physical state and colour	Structure
XX′1	ClF	colourless gas	–
	BrF	pale brown gas	–
	IF^a	detected spectroscopically	–
	BrCl^b	gas
	ICl	ruby red solid (α-form)	–
	Brown	red solid (β-form)	–
	IBr	black solid	–
XX′3	ClF3	colourless gas	Bent T-shaped
	BrF3	yellow green liquid	Bent T-shaped
	IF3	yellow powder	Bent T-shaped
	ICl3^c	orange solid	Bent T-shaped
XX′5	IF5	colourless gas but solid below 77 K	Square pyramidal
	BrF5	colourless liquid	Square pyramidal
	ClF5	colourless liquid	Square pyramidal
XX′7	IF7	colourless gas	Pentagonal bipyramidal

^a - Very unstable; ^b - The pure solid is known at room temperature; ^c - Dimerises as Cl–bridged dimer (I₂Cl₆)

Ø These molecules are covalent and diamagnetic in nature.

Ø The bonds formed between these compounds are more reactive than diatomic halogen bonds.

Ø The physical properties of these molecules are transitional between its constituents.

Ø The molecular structure of AX₃ molecules is bent T shaped, an AX₅ molecule is square or pyramidal and the structure of AX₇ is bipyramidal or pentagonal.

Ø The bond length depends upon the size of the constituent halogens.

Ø The molecule which consists of lighter group 17 elements is fairly colorless but one which is made up of higher halogens is deeper in color which is due to the rise in the molecular weight.

Uses

Ø These are used as non-aqueous solvents.

Ø They are used as a catalyst in few reactions.

Ø UF₆ which is used in the enrichment of ²³⁵ U is produced by using ClF₃ and BrF₃.

U (s) + 3ClF₃ (l) → UF₆ (g) + 3ClF (g)

Ø These are used as fluorinating compounds.