Dielectric relaxation of α-cyclodextrin-polyiodide complexes (α-cyclodextrin)[sub 2] · LiI[sub 3] · I[sub 2] · 8H[sub 2]O and (α-cyclodextrin)[sub 2] · Cd[sub 0.5] · I[sub 5] · 26H[sub 2]O.

The frequency and temperature dependence of real (ε[sup ′]) and imaginary (ε[sup ′′]) parts of the dielectric constant of polycrystalline complexes (α-CD)[sub 2] · LiI[sub 3] · I[sub 2] · 8H[sub 2]O and (α-CD)[sub 2] · Cd[sub 0.5] · I[sub 5] · 26H[sub 2]O (α-CD=α-cyclodextrin) has been investigated over the frequency and temperature ranges of 0-100 kHz and 120-300 K. The dielectric behaviour is described well by Debye type relaxation (α-dispersion). Both systems exhibit an additional Ω dispersion at low frequencies which is attributed to ionic conductance and is much greater in the case of Li due to the greater mobility of cations Li[sup +]. The temperature dependence of ε′ reveals the existence of two kinds of water molecule in the case of the (α-CD)[sub 2] · Cd[sub 0.5] · I[sub 5] · 26H[sub 2]O complex; these can be classified as tiqhtly bound and easily movable water molecules that cause two steps in ε ′ versus T plots. In the case of the (α-CD)[sub 2 ]· LiI[sub 3] · I[sub 2] · 8H[sub 2]O complex the water molecules are tightly bound and as a result only one step is observed in these graphs. These finding are also confirmed from the ε[sup ′′][sub max] versus T plots, which exhibit the same number of steps with ε[sup ′], and from calorimetric measurements. The order-disorder transition or the transformation of normal hydrogen bonds to flip-flop type has been observed as a peak in ε[sup ′′] versus T plots that is more intense and narrow in the case of Li and less high but more broad in Cd. The relaxation time varies in a ∧-like curve (from 120 K to 240 K) and rises rapidly for temperatures greater than 240 K, indicating the existence of a new process involving the breaking of hydrogen bonds (normal or flip-flop type). The calculated values of activation energy (0.35-0.62 k[sub B]T trans) reveal the greater stability of the Li compared with the Cd complex. The starting value of 8.2-8.4 µs for τ is the same as observed in β-CD complexes with guest 4-t-butylbenzyl alcohol (TERB). However, the activation energies of these are greater (1.1-1.7 k[sub B]T trans), indicating greater stability for β-CD complexes. [ABSTRACT FROM AUTHOR]