Crystal Structures of Nylon–Iodine Complexes

The crystal structures of iodine complexes of nylon-6 and nylon-66 samples were proposed on the basis of 2-dimensional wide-angle X-ray diffraction data analysis combined with the observed polarized Raman spectral data and the density functional theoretical calculations. As reported in our previous paper (Macromolecules, 2024, 57, 2260), the skeletal chains of nylon were found to be contracted about 5% from the fully extended conformations, which are caused by the trans-to-skew torsional angle change around CH₂–amide bonds so that the charge transfer occurs from the iodine ion to N–H group. The iodine ion rods are sandwiched between the nylon chains alternately. The I₅^– and I₃^– ion rods are oriented, respectively, along the nylon chain axis and in the direction approximately perpendicular to the chain axis. The sandwich packing structure is different among complex I and complex II, which are formed by immersing nylon-6 sample in the iodine solution of different concentration (0.5 and 3 M, respectively). The similar structure model was proposed also for nylon-66. The thus-constructed crystal structure models reproduced the observed X-ray diffraction patterns quite well. By a comparison of the X-ray diffraction data observed for the doubly oriented samples, the geometrical relation was revealed between the pristine nylon crystal and the nylon–iodine complexes.