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.