Javier De Mendoza and his research team, Institute of Chemical Research of Catalonia (ICIQ), Tarragona, Spain, have synthesized unique octahedral and icosahedral anionic UOFs (Uranyl Organic Frameworks) from calixarenes, carboxylates and uranyl (UO₂²⁺) at room temperature. Octahedral and icosahedral anionic metallocages of nanoscopic dimensions are formed with an unusually small number of components.

Unlike most metallocages reported to date, the metals in these nanoscopic assemblies are not located at the corners or the edges of the resulting polyhedral but on the faces instead, acting both as a gluing element for the assembly of the components and a functional key substructure.
This novel arrangement allows host-guests interactions inside the cage and encapsulation of polycationic or electron deficient molecules.

The size of the calixarenes defines and dictates the shape and the size of the resulting globular assemblies in an univocal fashion:

• 6 calix[4]arene subunits promote self-assembly into hexameric cages with an available spherical volume of ca. 940 ų
• 12 calix[5]arene subunits promote self-assembly into icosahedral structures with an available spherical volume of more than 7000 ų.

These anionic polyhedral have interesting photoluminescent, photoelectric and photocatalytic properties that can lead to efficient degradation of organic molecules, including pollutants, under UV irradiation.

_{Image: UOF with inscribed sphere of ca. 7338 Å}³_{. © ICIQ}

• Giant regular polyhedra from calixarene carboxylates and uranyl,
  Sara Pasquale, Sara Sattin, Eduardo C. Escudero-Adán, Marta Martínez-Belmonte, Javier de Mendoza,
  Nature Communic. 2012.
  DOI: 10.1038/ncomms1793