High density flip-flop hydrogen-bonding networks in the β-cyclodextrin heptaiodide inclusion complexes with Bi3+ and Te4+ ions. Combined dielectric relaxation, Raman scattering and thermal analysis

The polycrystalline inclusion complexes (β-CD)2·TeI7·17H2O and (β-CD)2·BiI7·17H2O have been investigated via dielectric spectroscopy over a frequency range of 0-100 kHz and the temperature range of 140-425 K. Furthermore, a DSC study was carried out in the range of 273-423 K, whereas the Raman spectra (303-393 K) of β-Te were compared to the previously examined ones of β-Bi. In the case of β-Te an important percentage of normal H-bonds is transformed into flip-flop ones (Ttrans = 216.8 K) as it comes out by the corresponding ε′ (T), ε″ (T) and φ(T) variations at T < 250 K (Δε′ = 18.6, ε″max = 4.8, φmin = 69.9°). In β-Bi the greatest percentage of normal H-bonds is transformed into those of the flip-flop type (Ttrans = 223.6 K, Δε′ = 49.6, ε″max = 16, φmin = 58.6ο) producing a disordered H-bonding network of a much higher density than that of β-Te. At T > 250 K, the ac-conductivity (lnσ vs. 1 / T) of these systems follows an Arrhenius behaviour with activation energies 0.54 and 0.46 eV for β-Te and 0.38, 0.68 and 0.58 eV for β-Bi. This exponential increment reflects the combined contributions of the water network, the oscillating cations and the dehydration process. The abrupt increase of the ac-conductivity at T > 398.5 K is caused by the sublimation of iodine. The temperature-dependent Raman spectra of β-Te exhibit the band shift of 178 → 172 cm− 1 which is identical to that of β-Bi, implying a similar elongation of their I2 units. The high density flip-flop hydrogen-bonding network in the latter complex seems to play a key role in limiting the Lewis base character of I−3.