A Uniquely Structured Heteronuclear Cluster Cage with Anion-Templated Pentagons and Hexagons

Constructing structurally sophisticated molecules with interesting properties is the goal of supramolecular chemistry. Herein, two heterometallic clusters, formulated respectively as [Gd₁₃₆Ni₈₄L₁₀₆(μ₆-C₂O₄)₁₂(μ₅-NO₃)₁₂(μ₃-OH)₁₇₆(μ-OH)₂₆(μ₄-C₂O₄)₃(H₂O)₁₀₆]Cl₁₂₀·49H₂O·90MeOH (Gd₁₃₆Ni₈₄, H₂L = N-methyliminodiacetic acid) and [Tb₁₃₆Ni₈₄L₁₀₆(μ₆-C₂O₄)₁₂(μ₅-NO₃)₁₂(μ₃-OH)₁₇₆(μ-OH)₂₆(H₂O)₁₁₄]Cl₁₂₆·50H₂O·130MeOH (Tb₁₃₆Ni₈₄), were obtained by the cohydrolysis of Ln³⁺ (Ln = Gd, Tb) and Ni²⁺ in the presence of H₂L and triethylamine. The essentially isostructural cationic cluster cages are constructed by coexisting pentagons and hexagons whose formation is respectively templated by nitrate and oxalate ions. Rather than the desired buckminsterfullerene structure, the clusters are of a truncated tetrahedral structure due to the unique disposition of the polygonal building units that are structurally distinct from those in a regular fullercage. Cluster Gd₁₃₆Ni₈₄ maintains its structural integrity in solution as evidenced by the results of mass spectroscopic and electron microscopic studies. Its isothermal magnetic entropy change is 43.91 J·kg^-1·K^-1 at 3.0 K and 7.0 T, placing it among the high-performing lanthanide-containing clusters possibly useful for magnetic cooling.