Complex-within-complex assemblages from {M([2.2.2]cryptand)(H2O)2}2+ (M = Sr, Ba) and {UO2(p-tert-butyl[3.1.3.1]homooxacalixarene – 4H)}2−

Abstract

The reaction between p-tert-butyl[3.1.3.1]homooxacalixarene, currently named p-tert-butyltetrahomodioxacalix[4]arene, LH₄, and uranyl salts in the presence of [2.2.2]cryptand and the alkaline-earth metal cations Sr²⁺ or Ba²⁺ gives the complexes [{Sr[2.2.2](H₂O)₂} ⊂ {UO₂(L)}]·H₂O·4CH₃OH and [{Ba[2.2.2](H₂O)₂} ⊂ {UO₂(L)}]·4H₂O·4CH₃OH, respectively. In the crystal, the uranyl ion is located in the tetra-phenoxide site of the homooxacalixarene in the cone conformation and linked to the cryptate by a water⋯oxo hydrogen bond. The cryptate is included in the uranyl complex cavity and the infinite chains formed through hydrogen bonds and other weak interactions are thus novel examples of complex-within-complex supramolecular assemblages. By contrast, the addition of triethylamine to the reaction mixture leads to the compound {Ba[2.2.2](H₂O)₂}{[HNEt₃] ⊂ [UO₂(L)]}₂·5H₂O, in which the triethylammonium cation replaces the cryptate in the cavity, the cryptate simply acting as a link between two uranyl complex moieties through water⋯phenoxide hydrogen bonds. The assemblage [{Ba[2.2.2](H₂O)₂} ⊂ (LH₃)](LH₃)·2H₂O, including the uncomplexed anion LH₃⁻, is also described. Analysis of the NMR spectra of the three uranyl complexes indicates that the cryptate and the [UO₂(L)]²⁻ moieties do not specifically interact in dilute (CD₃)₂SO solution, while the supramolecular arrangement of {Ba[2.2.2](H₂O)₂}{[HNEt₃] ⊂ [UO₂(L)]}₂·5H₂O is largely retained in halogenated solvents.