PARTIAL MOLAR VOLUME OF 18-CROWN-6 COMPLEX-IONS WITH ALKALI-METAL IONS IN METHANOL

The sedimentation potential (SP), molar conductivities and partial mol ar volumes at infinite dilution of salts (NaCl, KCl and CsCl) in metha nol containing 18-Crown-6 (18 C 6) have been measured. By combining SP , transference numbers and limiting partial molar volumes of salts con taining 18 C 6, single-ion volumes at infinite dilution of [18 C 6-M+] complex ion and Cl- ion have been evaluated. The single-ion partial m olar volume of chloride ion is in fair agreement with that observed fo r alkali-metal-salts in methanol not containing 18 C 6. This fact sugg ests clearly that the charge of the alkali-metal ion trapped in the 18 C 6 cavity is effectively shielded by 18 C 6. The biggest volume chan ge is shown for the 18 C 6 complex ion with K+ among all the alkali-me tal ions studied.