Frequencies of the quantized motion of cations encaged in cyclic poly ether (crown) systems have been determined from solvent-and anion-independent bands in the far ir spectra of dissolved crown-alkali-metal-salt complexes in pyridine and DMSO. The analysis of the forces with which the cations are encaged shows that the Na+-crown and K+-crown forces are nearly equal for dibenzo-18-crown-6, and that cation selectivity in these cases does not derive from differences in ion-crown encagement forces. The forces between cations and solvent molecules (DMSO, pyridine) are evaluated from cation-motion frequencies which are shown to be independent of the nature of the counterion in several salt solutions. The combined results from solvated and crown-encaged cations are shown to establish the basis for evaluation of molecular scale forces involving antibiotic-cation complex species postulated to be responsible for ion-selective transport properties. n work recently reported from this laboratory2-5 and others,6-16 it has been demonstrated that vibrational bands due to quantized motion of simple ions in solu-
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