Thiacalix[4]arene: New protection for metal nanoclusters.

Surface organic ligands are critical for the formation and properties of atomically precise metal nanoclusters. In contrast to the conventionally used protective ligands such as thiolates and phosphines, thiacalix[4]arene has been used in the synthesis of a silver nanocluster, [Ag35(H2L)2(L)(C≡CBu(t))16](SbF6)3, (H4L, p-tert-butylthiacalix[4]-arene). This is the first structurally determined calixarene-protected metal nanocluster. The chelating and macrocyclic effects make the thiacalix[4]arene a rigid shell that protects the silver core. Upon addition or removal of one silver atom, the Ag35 cluster can be transformed to Ag36 or Ag34 species, and the optical properties are changed accordingly. The successful use of thiacalixarene in the synthesis of well-defined silver nanoclusters suggests a bright future for metal nanoclusters protected by macrocyclic ligands.