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Series of lanthanide‐containing metallic coordination complexes are frequently presented as structurally analogous, due to the similar chemical and coordinative properties of the lanthanides. In the case of chiral (Ln^III[15‐MC_N(L‐pheHA)‐5])³⁺metallacrowns (MCs), which are well established supramolecular hosts, the formation of dimers templated by a dicarboxylate guest (muconate) in solution of neutral pH is herein shown to have a unique dependence on the identity of the MC's central lanthanide. Calorimetric data and nuclear magnetic resonance diffusion studies demonstrate that MCs containing larger or smaller lanthanides as the central metal only form monomeric host‐guest complexes whereas analogues with intermediate lanthanides (for example, Eu, Gd, Dy) participate in formation of dimeric host‐guest‐host compartments. The driving force for the dimerization event across the series is thought to be a competition between formation of highly stable MCs (larger lanthanides) and optimally linked bridging guests (smaller lanthanides).

Seven dimeric metallacrowns (MC) based on Ln[12‐MC_M(III)N(shi)‐4], where Ln^III=Dy, Ho, Yb, or Y, M^III=Mn or Ga, and shi³⁻is salicylhydroximate, have been synthesized and characterized by single‐crystal X‐ray diffraction, and for the dysprosium‐manganese dimers, the magnetic properties have been measured. In each dimer two Ln[12‐MC_M(III)N(shi)‐4] units are linked by four bridging dicarboxylate anions (isophthalate, trimesate, dinicotinate, or 2,2′‐dithiodibenzoate). Three different countercations (sodium, gallium(III), or pyridinium) were used to maintain charge balance of the dimer. While pyridinium does not bind to the dimer, the choice of the dicarboxylate dictates where the countercations Na⁺or Ga^IIIbind. With isophthalate and trimesate, the sodium ion binds to the central MC cavity opposite of the Ln^III, and with dinicotinate the sodium or gallium(III) ions bind to the pyridyl nitrogen of the dinicotinate. All three Dy₂Mn₈dimers exhibit an out‐of‐phase magnetic susceptibility signal consistent with a shallow barrier to magnetization relaxation.