Conductivity properties of thiourea- and urea-halogen inclusion compounds with diquinuclidinium cation as guest

Abstract

Thiourea and urea can modify their typical host properties to form new ternary polymolecular anionic halogen hosts in which the diquinuclidinium cation is included. A comparative study of the proton conductivity properties of this kind of inclusion compounds is presented. The hexagonal binary inclusion compound [quinuclidine]3thiourea 1 was taken as reference. The study shows the conductivity properties of [quinuclidine2H]+[thiourea2Cl]- 2, [quinuclidine2H]+[thiourea2Br]- 3, [quinuclidine2H]2 2+[thiourea2I2]2- 4, [quinuclidine2H]+[urea5Cl]- 5, [quinuclidine2H]+[urea2Br]- 6, and [quinuclidine2H]+[urea2I]- 7. Ionic conductivities of all the compounds in pellets, and of 2 and 3 in large single crystals were measured by electrochemical impedance spectroscopy (EIS). Anisotropic conductivity behaviour in crystals of adequate dimensions of 2 and 3 was detected. The conductivity values of 2 and 3 in the crystals were 2.19x10-4 and 6.03x10-6 (S/cm), respectively, in the assumed channel direction, and 2.42x10-6 and 8.27x10-9 (S/cm), respectively, in the perpendicular direction to the former, at 298 K. Conductivities at room temperature of the thiourea-halide derivatives in pellets show a changing behaviour from insulator (10-11 S/cm) for 2, 3 and 4 measured in vacuum, to semiconductor (10-7-10-8S/cm) for the thiourea-halide derivative measured at atmospheric pressure. For the urea-halide system the highest conductivity value corresponds to derivative 7 (8.66x10-5 S/cm) at atmospheric pressure, and the lowest to derivative 5 (5.48x10-7 S/cm) measured in vacuum. Comparisons considering structural aspects are also discussed.