Theoretical Study on Structure and 18O Isotope Effect on Vibrational Spectra of Iodosylbenzene Oligomer

Ten geometries of iodosylbenzene oligomer HO-(PhIO)(n)-H (n=1 similar to 10) model compounds were investigated by LDA-PWC method. The calculated geometries show that the PhIO unit in iodosylbenzene oligomer has a T-shaped structure, and both I-O bond lengths of I-O chain are nearly equal. Due to the torsion of I-O chain, iodosylbenzene oligomer exhibits a helical geometry. To obtain a more accurate and steady geometry, the structure of HO-(PhIO)(6)-H was also investigated by B3LYP calculations. Results show that the I-O bond mean length is 0.2089 nm with only 0.0007 nm standard deviation. IR spectral calculation results show that the vibrational frequencies between 600 similar to 400 cm(-1) will shift to lower frequencies upon the O-18 substitution, which is in accordance with the experimental observation. Vibrational mode analysis indicates that these bands are related to oxygen atom vibrations. The observed O-18 sensitive IR bands of 591/566 cm(-1) and 443/436 cm(-1) (O-16/O-18) correspond to the calculated bands of 590.409/557.788 cm(-1) and 460.627/439.158 cm(-1) (O-16/O-18) respectively, and the former was ascribed to the symmetric stretching mode v((I-O-I)) of iodosylbenzene oligomer, and the latter to the absymmetric stretching mode V(I-O-I).