Modern inorganic chemistry

GROUP VII: THE HALOGENS 345

(a) FeCl 3 4- 6H 2 O -> [Fe(H 2 O) 6 ]^3 + + 3C1"

[Fe(H 2 O) 6 ]^3 + + H 2 O ^ [Fe(H 2 0) 5 (OH)]2+ + H 3 O+ etc.

(b) BC1 3 + 3H 2 O -> H 3 BO 3 + 3HC1

The hydrolysis of phosphorus tribromide or triiodide is used in

the preparation of hydrogen bromide and hydrogen iodide res-

pectively:

PBr 3 + 3H 2 O -» H 3 PO 3 + 3HBrT

PI 3 + 3H 2 O -> H 3 PO 3 + 3HIT

Complex halides

Halogens can act as ligands and are commonly found in complex
ions; the ability of fluorine to form stable complex ions with
elements in high oxidation states has already been discussed (p. 316).
However, the chlorides of silver, lead(II) and mercury(I) are worthy
of note. These chlorides are insoluble in water and used as a test for
the metal, but all dissolve in concentrated hydrochloric acid when
the complex chlorides are produced, i.e. [AgCl 2 ]~, [PbCl 4 ]^2 ~ and
[HguCl 3 ]~, in the latter case the mercury(I) chloride having also
disproportionated.

INTER HALOGEN COMPOUNDS AND POLYHALIDES

There are four types of interhalogen compound:

Type XX : C1F, BrF, BrCl, IC1

They are monohalides, for example C1F is

called chlorinemonofluoride.

Type XX' 3 : C1F 3 , BrF 3 , IC1 3 (The trifluoride,

trichloride)

Type XX' 5 : BrF 5 , IF 5 (The pentafluorides)

Type XX^: IF 7 (the only example), iodine heptafluoride

Iodine monochloride, IC1, monobromide, IBr, and trichloride, IC1 3 ,
are solids at room temperature, the remainder being volatile
liquids or gases. They are made by the direct combination of the
halogens concerned. All are covalent with the larger halogen
occupying a central position. With the exception of iodine penta-
fluoride, IF 5 , they are extremely reactive, behaving (like halogens)
as oxidising agents and reacting with water. The two most important
mterhalogen compounds are the trifluorides of chlorine, C1F 3 (the