A conductance study of 18-crown-6 and dibenzo-18-crown-6 complexes with K+ in various solvents.

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Limiting ionic molar conductivities (λ°) of 18-crown-6 (18C6) and dibenzo-18-crown-6 (DB18C6) complexes with K+ in several protic and aprotic solvents have been determined at 25 °C. The crystal ionic radius of 18C6 complex with K+ is nearly identical with that of tetrabutylammonium ion ((n-C4H9)4N+). For CH3OH, the mobility of the 18C6 complex with K+ is nearly equal to that of (n-C4H9)4N+. However, for H2O, the former is much larger than the latter, but the contrary is true for aprotic solvents. Walden products of 18C6 complexes with K+ for the solvents are nearly equal to each other. For acetonitrile and DMSO, the λ° value of the DB18C6 complex with K+ is smaller than those for the tetrapentylammonium ion ((n-C5H11)4N+) and for the tetraisopentylammonium ion ((i-C5H11)4N+). For nitrobenzene and propylene carbonate, that of the DB18C6 complex with K+ is smaller than those of (n-C5H11)4N+ and (i-C5H11)4N+, respectively. In contrast to the case of the aprotic solvents, the λ° value of the DB18C6 complex with K+ for CH3OH is nearly equal to those of (n-C5H11)4N+ and (i-C5H11)4N+. Walden products of the DB18C6 complexes with K+ for the solvents are nearly equal to each other. From the above data, it appears that a solute which contains a unit of 18C6 in its structure does not enforce a hydrogen-bonded structure for a protic solvent.
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