Six oxygen atoms Eighteen in a circle A cavity prepared A position to occupy Crown ether Crown ether Select the ion Close the ring Crown ether Crown ether Perfect coordination Everything in place Size determines entry Geometry decides No need for permission No reason to explain Recognition Coordination Complexation Separation R — O — R R — O — R Select the ion Maintain the ring R — O — R R — O — R Perfect coordination Everything in place Eighteen Crown Six The cavity remains.
