Two interconverting pentaiodide forms in the cyclomaltohexaose (α-cyclodextrin) polyiodide inclusion complex with sodium ion: dielectric and Raman spectroscopy studies Original Research Article

The polycrystalline inclusion complex of cyclomaltohexaose, (α-CD)2·NaI5·8H2O, has been investigated via dielectric spectroscopy over a frequency range of 0–100 kHz and the temperature range of 125–450 K. Additionally, a Raman spectroscopy study was accomplished in the temperature ranges of (i) 153–298 K and (ii) 303–413 K. The ln σ versus 1/T variation revealed the order–disorder transition of some normal hydrogen bonds to those of a flip-flop type at 200.9 K. From 278.3 up to 357.1 K, the progressive transformation (H2O)tightly bound → (H2O)easily movable takes place resulting in an Arrhenius linear increment of the ac-conductivity with activation energy Ea = 0.32 eV. In the range of 357.1–386.1 K a second linear part with Ea = 0.55 eV is observed, indicating the contribution of sodium ions via the water-net.The rapid decrease of the ac-conductivity at T > 386.1 K is due to the removal of the water molecules from the crystal lattice, whereas the abrupt increase at T > 414.9 K is caused by the sublimation of iodine.The Raman bands at 160 and 169 cm−1 ind