Charge-transfer complexes. Part VIII. Cation dependence of the charge-transfer band of the iodide–trinitrobenzene complex

In highly polar solvents the charge-transfer band of the s-trinitrobenzene–iodide ion complex is unaffected by changes in the cation. In solvents of low polarity where iodide exists predominantly within an ion pair, there is a marked dependence of the charge-transfer band position on the size of the cation. In some mixed solvents, two bands may be observed corresponding to the free-ion and ion-pair forms of the complex and there is evidence of selective solvation of the two forms.