Knowledge Bank

“Changes in the infrared spectrum of ICN as this molecule forms charge-transfer complexes of different strength have been studied. The changes in the I-C stretching motion are similar to those observed in the I-CI stretching motion as ICI forms charge-transfer $complexes.2$ These are; (1) a decrease in frequency; (2) an increase in the half-intensity width; (3) a marked increase in intensity. These changes can be correlated with increasing strength of interaction, as measured by the formation constant of the complex. In contrast with this behaviour, the changes in the I-C-N bending frequency and in the C-N stretching motion, which are much less pronounced, show little correlation with the strength of the complex. The similarity between the changes observed in the I-C-N vibrations due to the formation of charge-transfer complexes and the changes observed in the O-H frequencies on hydrogen-bond formation are quite striking. The correlation plots of Huggins and $Pimented\ast$ have been modified to show this similarity. It seems to be possible to explain all these changes in terms of a slightly modified “charge-transfer modul”.”