The effect of the anion in a crown ether-cation structure is examined by co
mparing the structure of [{Na(C20H36O6)}(ReO4)] with one containing the sam
e crown ether and cation, but a different anion. The title compound shows t
hat the crown ether does not form an ideal cavity for sodium, as the Na-O b
ond lengths vary from 2.470(4) (O3) to 2.863 (4) Angstrom (O1).