Generalized Synthesis of Calixarene-Based High-Nuclearity M4n Nanocages (M = Ni or Co; n = 2–6)

Abstract

A family of high-nuclearity M4n (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) nano...