Actinide complexes of the calixarenes. Part 1. Syntheses and crystal structures of bis(homo-oxa)-p-tert-butylcalix[4]arene and its uranyl ion complex

Abstract

Interaction of the uranyl ion with the potentially quinquedentate calixarene bis(homo-oxa)-p-tert-butylcalix[4]arene, C₄₅H₅₈O₅(H₄L), in the presence of amine bases results in the formation of the red-brown, anionic complex [UO₂(L)]^2–. Crystal-structure determinations of the hydrated triethylammonium salt of this complex [monoclinic, space group C2/c(C_2h⁶, no. 15), a= 29.81(2), b= 16.653(7), c= 26.38(2)Å, β= 115.47(4)°, Z= 8, R= 0.049 for 6608 ‘observed’ reflections] and of the dimethylformamide adduct of the free ligand [monolinic, space group P2₁/m(C_2h², no. 11), a= 9.701(1), b= 25.108(9), c= 9.230(3)Å, β= 95.97(2)°, Z= 2, R= 0.067 for 1749 ‘observed’ reflections] show that the ligand adopts a very similar ‘cone’ conformation in both instances, and that the uranium–ligand interaction is primarily through the four phenoxide donor atoms, with only a remote (and presumably weak) contact between the uranium and ether-oxygen atoms. One of the triethylammonium counter cations is included within the cone of the co-ordinated ligand in a very similar way to the inclusion of dimethylformamide by the free ligand, and ¹H NMR spectroscopy indicates that this inclusion persists in solution. Uranyl ion luminescence is quenched completely in solutions of the complex at room temperature.