Generalized Synthesis of Calixarene-Based High-Nuclearity M_4<i>n</i> Nanocages (M = Ni or Co; <i>n</i> = 2–6)

A family of high-nuclearity M_4<i>n</i> (M = Ni or Co, <i>n</i> = 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 (<b>1</b> and <b>2</b>, <i>n</i> = 2), M₁₂ (M = Ni (<b>3</b>) and Co (<b>4</b>), <i>n</i> = 3), M₁₆ (M = Ni (<b>5</b>) and Co (<b>6</b>), <i>n</i> = 4), Co₂₀ (<b>7</b>, <i>n</i> = 5), and Co₂₄ (<b>8</b>, <i>n</i> = 6) coordination nanocages. Structural analyses reveal that the metallic cores of <b>1</b> and <b>2</b> are arranged in chair conformation, while compounds <b>3</b>–<b>6</b> 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 (<b>7</b>) is the only one in this family with an open-shell structure, which can be thought of as a truncated octahedral Co₂₄ (<b>8</b>) nanocage cutting one face. Furthermore, the magnetic behaviors of <b>1</b>–<b>8</b> have been investigated, suggesting the existence of strong antiferromagnetic interactions between magnetic centers for all title coordination cages.