Anion-Guided Hierarchical Assembly of Heterometallic Clusters

Anions are important as templates for the construction of many structurally sophisticated and functional supramolecular architectures. Deciphering the specific role of such templates remains a great challenge due to the unique characteristics of anions. Herein, three heterometallic Ce-Ni clusters, namely, [Ce₂₄Ni₃₆L₃₆(μ₄-OAc)₆(OH)₅₂(Cl)₈]Cl₆·110H₂O (Ce₂₄Ni₃₆, OAc = acetate ion, L = N-methyliminodiacetate), [Ce₁₇Ni₂₇L₂₇(μ₆-C₂O₄)₆(OH)₁₅(Cl)₁₆(H₂O)₁₉](ClO₄)₂Cl₆·45H₂O (Ce₁₇Ni₂₇), and [Ce₂₁Ni₃₀L₃₀(μ₆-C₂O₄)₂(μ₄-OAc)(OH)₃₂(Cl)₁₅(H₂O)₁₄](ClO₄)₄Cl₇·55H₂O (Ce₂₁Ni₃₀), were obtained and structurally characterized; the formation of these cage-like clusters was assisted, respectively, by acetate, oxalate, and a combination of the two as templates. Structural analyses generate key information on the anion-directed hierarchical assembly, starting from a primary building block of {CeNi₃} to two anion-specific secondary building blocks (SBUs)─the tetragonal {Ce₄Ni₈(OAc)} and the pentagonal {Ce₅Ni₉(C₂O₄)}. Further assembly steps are guided by these curved SBUs, affording a truncated octahedral Ce₂₄Ni₃₆ and a lantern-like Ce₁₇Ni₂₇, with acetate and oxalate being the sole template, respectively. The combined use of acetate and oxalate produced Ce₂₁Ni₃₀, a cluster with an unprecedented structure viewable as a hybrid of a truncated octahedron and a dodecahedron.