Electronic and infrared spectral and thermal studies on the molecular complex of dibenzo-18-crown-6 and iodine

The interaction of the crown ether dibenzo-18-crown-6 (DBC) with iodine has been studied in CHCl3 at room temperature. The charge-transfer absorptions, far infrared and thermal measurements of the formed charge-transfer complex were recorded and discussed. The results obtained show the formation of the pentaiodide complex with the general formula [(DBC)]+ I5−. The pentaiodide ion, I5−, is described as I3−(I2) confirmed by the observation of the characteristic absorptions for I3− ion around 365 and 290 nm. In addition, the far infrared spectrum of the solid complex shows the three vibrations of I3− unit is at 141, 113 and 71 cm−1 assigned to νas(I-I) and νs(I-I) and δ(I3−), respectively, while the band related to the vibration of I2 unit is observed at 180 cm−1. Vibration analysis of the obtained data shows that the symmetry of I3− unit could be non-linear with C2v symmetry. The structure of the formed pentaiodide complex was further supported by thermal gravimetric analysis measurements.