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The frequency and temperature dependence of the real (ε′) and imaginary (ε″) parts of the dielectric constant of the polycrystalline complexes (α-CD) 2 ·BaI 2 ·I 2 ·8H 2 O and (α-CD) 2 ·KI 3 ·I 2 ·8H 2 O (α-CD = α-cyclodetrin) have been investigated over the frequency and temperature ranges 0-100 kHz and 120-300 K, respectively. The temperature dependences of ε ′, ε ″ and the phase shift ϕ show two steps, two peaks and two minima, respectively, revealing the existence of two kinds of water molecule, the tightly bound and the easily movable water molecules, in both complexes. The first peak of ε ″( T ) or the first minimum of ϕ ( T ) presents the transformation of flip-flop hydrogen bonds to the normal state. The second ε ″ ( T ) peak or ϕ ( T ) minimum corresponds to the easily movable water molecules or to a partial transformation of tightly bound to easily movable water molecules. For T > 270 K both samples show semiconductive behaviour with energy gaps of 1.84 eV for the (α-CD) 2 ·BaI 2 ·I 2 ·8H 2 O complex and 1.36 eV for the (α-CD) 2 ·KI 3 ·I 2 ·8H 2 O complex. The conductivity at room temperature decreases in the order: (α-CD) 2 ·BaI 2 ·I 2 ·8H 2 O > (α-CD) 2 ·LiI 3 ·I 2 ·8H 2 O > (α-CD) 2 ·KI 3 ·I 2 ·8H 2 O > (αCD) 2 ·Cd 0.5 ·I 5 ·26H 2 O. The relaxation time varies in a Λ-like curve (from 120 to 250 K) and rises rapidly for temperatures greater than 250 K, indicating the process of ionic movements. The activation energies around the transition temperature 0.98-1.09 k B T trans for (α-CD) 2 ·BaI 2 ·I 2 ·8H 2 O and 1.06-1.55 k B T trans for (α-CD) 2 ·KI 3 ·I 2 ·8H 2 O reveal the greater stability of the α-K complex against that of the α-Ba complex. [ABSTRACT FROM AUTHOR]

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]