Versatility of large homooxacalixarenes as ligands in polymetallic complexes: the case of UO22+ and p-tert-butyloctahomotetraoxacalix[8]arene

The coordination of uranyl ions in their complexes with p-tert-butyloctahomotetraoxacalix[8]arene (LH8) is strongly dependent on the synthesis conditions. Tetranuclear [(UO2)4O4(LH8)]×10MeOH (1) differs from the previously reported, octa-phenoxide one by the coordination of all the ether groups and the subsequent rotation of the tetra-uranate cluster with respect to the macrocycle. In the presence of pyridine, [(UO2)2(py)4(LH4)]×py (2) is formed, in which the partially deprotonated ligand is bound to two independent uranyl species by four phenoxide and two ether groups only, thus evidencing the decrease in nuclearity due to a coordinating base (pyridine) preventing cluster formation through bridging ions.