POLYHALIDES When the halide ions combine with the

POLYHALIDES Ø 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. v. Polyhalide ions: IBr 2 -, ICl 2 -, Cl. Br 2 -, Br. Cl 2 v. Polyhalide compounds : k. ICl 4, Na. IBr 4, NH 4 IBr 2, KI 3

Classification I)Simple Polyhalide I 2 + I------- I 3 II)Mixed Polyhalide 2 F 2 + Cl----- Cl. F 4Ø Polyhalides with more than two types of halogens are rare. Eg: Cs. FIBr 3, Cs. FICl, Rb. FICl 3, KCl. IBr

Preparation: • i)The simple polyhalides are prepared by the action of halogens on metallic halides. Ø KI + I 2 ------ KI 3 Ø KI + 2 Cl 2 ---- KICl 4 Ø NH 4 I + 2 I 2 ----- NH 4 I 5

• ii) The mixed polyhalide are prepared by the action of halogens or interhalogens on a solid metallic halide Ø Cs. Cl + 2 F 2 ---- Cs. Cl. F 4 Ø Na. Br + IBr---- Na. IBr 2 Ø KCl + ICl------ KICl 2 • iii) Polyhalides may also be obtained by the displacement of halogen with another Ø Cs. Br 3 + I 2 ------- Cs. IBr 2 + IBr Ø KIBr 2 + Cl 2 ---- KICl 2 + Br 2

Properties: I. They are coloured compounds having low Melting Points II. They are generally soluble in H 2 O, acetone , alcohol III. They are ionic compounds and tend to decompose on heating Ø Cs. I 3 ---- Cs. I+I 2 Ø Rb. Icl 2 ---- Rb. Cl + ICl

iv) Replacement properities A halogen in the polyhalide may be replaced by a more E. N. atom, but the central halogen is not replaceable IBr 2 - + Cl 2 ----- ICl 2 - + Br 2 v) Action of halogen The halogen may be directly added to the polyhalide ICl 2 - + Cl 2 ----- ICl 4 -