Cation‐Dependent Multilayered Host–Guest Assemblies Formed by a Xanthene‐Based Dinuclear Nickel(II) Macrocycle

A planar bis(saloph) nickel(II) macrocyclic host, L^2bNi₂, incorporating xanthene motifs and hexyl side chains, was synthesized to provide structural rigidity and solubility. Its ion recognition behavior toward alkali metal ions was investigated by ¹H NMR titration, mass spectrometry, and X-ray crystallography. With Na⁺, a 2:1 (host/guest) sandwich-type complex was formed at 0.5 equiv, which shifted to a monomeric 1:1 complex upon further Na⁺ addition. In contrast, larger alkali metal ions such as K⁺, Rb⁺, and Cs⁺ formed stable 2:1 (host/guest) dimeric complexes, whose sandwich structures remained intact even in the presence of excess cation, resulting in the formation of 2:2, 2:3, and 3:2 higher-order assemblies, unlike those of previously reported related macrocycles. X-ray analyses revealed a rare hexagonal planar coordination for Na⁺ and orthogonally stacked dimeric structures for the larger cations. Theoretical calculations support the experimental trends, showing that larger alkali metal ions favor 2:1 complexation due to reduced repulsive interactions between the metallomacrocycles. These findings demonstrate that the aggregation behavior of the metallomacrocycle is sensitively tuned by the size and coordination preferences of guest cations, highlighting the utility of preorganized, metal-based macrocycles in constructing dynamic, multivalent supramolecular architectures.