Macrocyclic molecule 1 that has two saloph coordination sites was designed and synthesized. The macrocycle 1 was easily converted into the corresponding metallohosts 2 and 3 by the reaction with nickel(II) and palladium(II), respectively. As expected from the molecular structure of these metallohosts having an 18-crown-6-like cavity, the nickel(II) metallohost 2 showed excellent binding affinity toward Na+, Ca2+, and Sr2+ to give 1:1 host-guest complexes. Preorganization effect due to the extremely rigid metal-containing macrocycle was suggested to be a major factor for the strong binding. Larger cations such as K+, Rb+, Cs+, and Ba2+ gave higher aggregated host-guest complexes such as 2(2)M, 2(3)M(2), and 2(4)M(3). Density functional theory calculations revealed that smaller metal ions do not occupy the center of each macrocycle in the sandwich structures 22M, while larger Cs+ simultaneously interacts with all the 12 oxygen donor atoms. On the basis of the interaction energy calculations, the preference for 2Na over 2(2)Na can be explained by destabilization of 2(2)Na due to the elongated Na-O bonds and repulsive three- body interactions. When the ionic radius of the guest ion increases (K+, Rb+, Cs+), this destabilization becomes less significant and the formation of sandwich complexes 2(2)M is favored. Such aggregation would significantly affect the physical and chemical properties of the metal complexes due to the interplane interactions between the metal centers.