Because of the difference in the electronegativity of iodine and chlorine, this molecule is highly polar and behaves as a source of I+.

Excess chlorine converts iodine monochloride into iodine trichloride in a reversible reaction: ICl has two polymorphs; α-ICl, which exists as black needles (red by transmitted light) with a melting point of 27.2 °C, and β-ICl, which exists as black platelets (red-brown by transmitted light) with a melting point 13.9 °C.

[3] Iodine monochloride is soluble in acids such as HF and HCl but reacts with pure water to form HCl, iodine, and iodic acid: ICl is a useful reagent in organic synthesis.

ICl will also add to the double bond in alkenes to give chloro-iodo alkanes.

When such reactions are conducted in the presence of sodium azide, the iodo-azide RCH(I)–CH(N3)R′ is obtained.