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Which crown ether forms a complex with lithium ions?
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The crown ether that forms a complex with lithium ions (Li⁺) is 12-crown-4.
The selectivity of a crown ether for a specific alkali metal cation is determined by the size of the ring. Because the lithium ion is smaller than other alkali cations, it fits into the smaller cavity provided by the 12-crown-4 molecule, which consists of 12 atoms in the ring, including 4 ether oxygen atoms.1