Electronic, infrared and Raman spectral studies on the molecular complex of N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane with iodine.

The molecular complexation reaction between iodine and the interesting mixed oxygen-nitrogen cyclic base N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DBTODAOD) has been studied spectrophotometrically in CH2Cl2, CHCl3, and CCl4. The results of photometric titrations and elemental analysis show that the DBTODAOD base:iodine ratio is 1:4 forming the heptaiodide complex [(DBTODAOD)I]+.I7-. The heptaiodide ion (I7-) is described as I3-(2I2) confirmed by the observation of its characteristic strong absorptions around 365 and 295 nm. In addition, the far infrared spectrum of the solid complex shows the three vibrations of I3- unit at 142, 104, and 62 cm(-1) assigned to nuas(I-I), nus(I-I) and delta(I-3), respectively, while the Raman spectrum shows the corresponding bands at 147 and 108 cm(-1) beside two other bands at 181 and 214 cm(-1) related to the vibration of the I2 unit and the first overtone of nus(I-I) of I3-, respectively. The structure of the formed heptaiodide complex was further supported by thermal gravimetric analysis measurements. Group theoretical analysis indicate that the triiodide unit (I3-) in I7- may be non-linear with C2v symmetry.