Editing Iodine (section)

===Charge-transfer complexes ===
[[File:Iodine-triphenylphosphine charge-transfer complex in dichloromethane.jpg|thumb|upright=1.8|right|I<sub>2</sub>•[[triphenylphosphine|PPh<sub>3</sub>]] charge-transfer complexes in [[dichloromethane|CH<sub>2</sub>Cl<sub>2</sub>]]. From left to right: (1) I<sub>2</sub> dissolved in dichloromethane – no CT complex. (2) A few seconds after excess PPh<sub>3</sub> was added – CT complex is forming. (3) One minute later after excess PPh<sub>3</sub> was added, the CT complex [Ph<sub>3</sub>PI]<sup>+</sup>I<sup>−</sup> has been formed. (4) Immediately after excess I<sub>2</sub> was added, which contains [Ph<sub>3</sub>PI]<sup>+</sup>[I<sub>3</sub>]<sup>−</sup>.<ref name="InorgChem">{{Housecroft3rd|page=541}}</ref>]]

The iodine molecule, I<sub>2</sub>, dissolves in CCl<sub>4</sub> and aliphatic hydrocarbons to give bright violet solutions. In these solvents the absorption band maximum occurs in the 520 &ndash; 540&nbsp;nm region and is assigned to a {{pi}}<sup>*</sup> to ''σ''<sup>*</sup> transition.   When I<sub>2</sub> reacts with Lewis bases in these solvents a blue shift in I<sub>2</sub> peak is seen and the new peak (230 &ndash; 330&nbsp;nm) arises that is due to the formation of adducts, which are referred to as charge-transfer complexes.<ref name="Greenwood806">Greenwood and Earnshaw, pp. 806–07</ref>