Knowledge Bank

The infrared intensities of the $\nu (I-CI),\nu (I-I)$ and $\nu (D-A)$ vibrational bands found in charge-transfer complexes of n and $\pi$ electron donors with $I2$ and ICl have been measured in benzene and n-heptane solutions. A Beckman IR-11 spectrometer was used together with a cell constructed of high density polyethylene. Pathlength calibrations have been carried out using bands of known intensity in pure liquid $CHCl2CCl4$ and benzene, and it has been shown that the pathlength variation when using such a cell is sufficiently small to give good Beers Law plots and intensity values with a random error of less than $\pm 12$. The results extend the $earlier1-2$ higher frequency intensity studies on complexes with $Br2,ICl$ and ICN. Quantitative confirmation that the intensity of the $\nu (N-I)$ vibration is significantly lower than that of the $\nu (I-Cl)$ vibration in the pyridine-ICl complex has been obtained, indicating a smaller vibronic $effect4$ in the former vibration.