Template trapping and crystal structure of the magic number (H2O)21 cluster in the tetrahedral hole of a nanoscale global ion packed in a face-centered cubic pattern.

A nanoscale global ionic cluster [Co(H(2)O)(6) [symbol: see text] Co(8)L(12)](6+) packed in a face-centered cubic pattern was constructed as a "host", in which a magic number (H(2)O)(21) cluster was captured and stabilized in the tetrahedral hole as a "guest".