“…On the other hand, when the macrocycle's cavity is larger than the cation, as would be the case with 18crown-6 or 30-crown-10 complex of Na + , the crown molecules will pucker to achieve the correct O-Na + binding distances. 42 Other factors are important, such as the cation charge and type, 43,44 number and type of donor atoms, 45 crown substituents, 46 and ring flexibility, 47 as well as the physical properties of a solvent. 48,49 The complexation usually takes place in a solvent where the complex could crystallize.…”