Generalized Synthesis of Calixarene-Based High-Nuclearity M_4n Nanocages (M = Ni or Co; n = 2–6)

A family of high-nuclearity M_4n (M = Ni or Co, n = 2–6) coordination nanocages constructed by M₄–calix­[4]­arene molecular building blocks (MBBs) with inorganic phosphate or organic phosphonate ligands have been isolated by solvothermal syntheses and characterized by single-crystal X-ray diffraction. This family can be divided into five structural types with an increase in the number of M₄–calix­[4]­arene MBBs, including Ni₈ (1 and 2, n = 2), M₁₂ (M = Ni (3) and Co (4), n = 3), M₁₆ (M = Ni (5) and Co (6), n = 4), Co₂₀ (7, n = 5), and Co₂₄ (8, n = 6) coordination nanocages. Structural analyses reveal that the metallic cores of 1 and 2 are arranged in chair conformation, while compounds 3–6 with closed-shell structures, where their ports are sealed by sodium ions, present the first examples of 2p-3d heterometallic metal–calixarene nanocages to our knowledge. The novel helmet-like Co₂₀ (7) is the only one in this family with an open-shell structure, which can be thought of as a truncated octahedral Co₂₄ (8) nanocage cutting one face. Furthermore, the magnetic behaviors of 1–8 have been investigated, suggesting the existence of strong antiferromagnetic interactions between magnetic centers for all title coordination cages.