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

Abstract

At T<250K, the polyiodide inclusion complex (α-cyclodextrin) 2Sr0.5I517H2O 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>250K, the AC-conductivity is dominated by the combinational contributions of the disordered water network, the mobile Sr 2+ 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. © 2010 Taylor & Francis