1. POLYHALIDES
When the halide ions combine with the halogen molecules or interhalogens,univalent ions are obtained .these are known as polyhalide ions and the compounds of these are known as polyhalides .
Polyhalide ions:
IBr2-, ICl2-, ClBr2-,BrCl2-
Polyhalide compounds : kICl4,NaIBr4,NH4IBr2,KI3

2. Classification I)Simple Polyhalide I2 + I------------- I3-
II)Mixed Polyhalide
2F2 + Cl  ClF4-
Polyhalides with more than two types of halogens are rare.
Eg: CsFIBr3,CsFICl,RbFICl3,KClIBr

3. Preparation:
i)The simple polyhalides are prepared by the action of halogens on metallic halides.
KI + I  KI3
KI + 2Cl  KICl4
NH4I + 2I  NH4I5

4. ii) The mixed polyhalide are prepared by the action of halogens or interhalogens on a solid metallic halide
CsCl + 2F  CsClF4
NaBr + IBr  NaIBr2
KCl + ICl  KICl2
iii) Polyhalides may also be obtained by the displacement of halogen with another
CsBr3 + I CsIBr2 + IBr
KIBr2 + Cl  KICl2 + Br2

5. Properties: They are coloured compounds having low Melting Points
They are generally soluble in H2O,acetone ,alcohol
They are ionic compounds and tend to decompose on heating
CsI  CsI+I2
RbIcl  RbCl + ICl

6. iv) Replacement properities
A halogen in the polyhalide may be replaced by a more E.N. atom,but the central halogen is not replaceable
IBr2- + Cl  ICl2- + Br2
v) Action of halogen
The halogen may be directly added to the polyhalide
ICl2- + Cl  ICl4-