Versatility of {M(30-crown-10)} (M = K+, Ba2+) as a guest in UO22+ complexes of [3.1.3.1]- and [3.3.3]homooxacalixarenes

Abstract

The reaction between p-R-[3.1.3.1]- or [3.3.3]homooxacalixarenes and uranyl salts in the presence of 30-crown-10 and the alkali or alkaline-earth metal cations K⁺ or Ba²⁺ gives various supramolecular assemblages characterized by “complex-within-complex” architectures. These can be of the simple nesting or sandwich types, as in [{Ba(30-crown-10)}{UO₂(L¹)}]·2H₂O·3CHCl₃ (L¹H₄ = p-tert-butyl[3.1.3.1]homooxacalixarene) and [{Ba(30-crown-10)}{UO₂(L⁴)}₂]·2CHCl₃ (L⁴H₃ = p-bromo[3.3.3]homooxacalixarene), respectively, with the cation held in the cavity of the homooxacalixarene complexes in cone conformation by weak interactions, but more original structures arise when uranyl-cation bonds are present. In [{Ba(30-crown-10)}{UO₂(L²)}] (L²H₄ = p-phenyl[3.1.3.1]homooxacalixarene), the barium ion included in the crown ether is bound to the uranyl oxo group located out of the calixarene cavity, resulting in the formation of a neutral species which self-organizes to form a columnar assembly by auto-inclusion. In [{K(30-crown-10)}{UO₂K(L¹)(H₂O)₃}]₂·6H₂O, the nesting-type subunit dimerizes around two oxo-bound potassium ions. Finally, the use of the coordinating solvent dimethylsulfoxide leads to the neutral complex [UO₂Ba(L³)(dmso)₂(MeOH)]₂ (L³H₄ = p-methyl[3.1.3.1]homooxacalixarene), in which the crown ether is absent and two oxo-, phenoxo- and ether-bound barium atoms ensure the dimerization of the uranyl complex.