Vasileios G. Charalampopoulos

An insight into the disorder properties of the α-cyclodextrin polyiodide inclusion complex with Sr2+ ion: dielectric, DSC and FT-Raman spectroscopy studies

At T < 250 K, the polyiodide inclusion complex (α-cyclodextrin)2·Sr0.5·I5·17H2O displays two separate relaxation processes due to both the frozen-in proton motions in an otherwise ordered H-bonding network and the order–disorder transition of some normal H-bonds to flip-flop ones. At T>250 K, the AC-conductivity is dominated by the combinational contributions of the disordered water network, the mobile Sr2+ ions, the polyiodide charge-transfer interactions and the dehydration process. The evolution of the Raman spectroscopic data with temperature reveals the coexistence of four discrete pentaiodide forms. In form (I) (I− 3·I2 ↔ I2·I− 3), the occupancy ratio (x/y) of the central I− ion differs from 50/50. In form (IIa) (I2·I− ·I2) x/y = 50/50, whereas in its equivalent form (IIb) (I2·I− ·I2) * as well as in form (III) (I− 3·I2), x/y = 100/0 (indicative of full occupancy). Through slow cooling and heating, the inverse transformations (I) → (IIa) and (IIa) → (I) occur, respectively.

Significant modification of the I(-)3 Lewis base character in the β-cyclodextrin polyiodide inclusion complex with Co2+ ion: an FT-Raman investigation.

The β-cyclodextrin (β-CD) polyiodide inclusion complex (β-CD)(2)·Co(0.5)·I(7)·21H(2)O has been synthesized, characterized and further investigated via FT-Raman spectroscopy in the temperature range of 30-120°C. The experimental results point to the coexistence of I(-)(7) units (I(2)·I(-)(3)·I(2)) that seem not to interact with the Co(2+) ions and I(-)(7) units that display such interactions. The former units exhibit a disorder-order transition of both their I(2) molecules above 60°C due to a symmetric charge-transfer interaction with the central I(-)(3) [I(2)←I(-)(3)→I(2)], whereas in the latter units only one of the two I(2) molecules becomes well-ordered above 30°C. The other I(2) molecule remains disordered presenting no charge-transfer phenomena. The Co(2+) ion induces a considerable asymmetry on the geometry of the I(-)(3) anion and a significant modification of its Lewis base character. Complementary dielectric measurements suggest no important involvement of H···I contacts in the observed modification of the I(-)(3) electron-transfer properties.