MOSSBAUER-EFFECT OF I-129 IN N-SIGMA AND PI-SIGMA CHARGE-TRANSFER COMPLEXES OF IODINE IN THE FROZEN SOLUTION

The Mössbauer effect of 129I was applied to investigate charge-transfer complexes of the n-σ and π-σ types in the carbon disulfide frozen solution at 16 K. In the case of n-σ type complexes such as triethylamine-iodine and pyridine-iodine, two chemical species of iodine, which correspond to the bridging and terminal iodines, were observed in the Mössbauer spectra. It is elucidated that a charge-transfer bond is described as a mixture of a four-electron three-center bond and a covalent bond involving dσpσ hybrid orbitals in the bridging iodine. On the other hand, for the π-σ type complexes such as benzene-iodine and methylated benzene-iodine the Mössbauer spectra show only one chemical species of iodine. The acceptor orbital of iodine is thought to be described by an spd hybrid orbital. That is, a small amount of s and d characters contributes to the formation of the charge-transfer bond. From the Mössbauer parameters the charge densities and the charge distributions of iodine in these complexes were obtained. © 1980 American Institute of Physics.